Drama Recs with Powerful Second Lead

I am the complete opposite of you! The day Asian dramas abolish their penchant for arbitrarily writing in second leads I'll dance in the streets naked. :) I also never suffer from 2nd lead syndrome, ever. Not even when the 2nd is a really nice guy/gal and the lead is a jerk. 

Why? Because as far as I can see most shows just insert a 2nd lead to create 'cheap' conflict, just so the lead can have a rival -- but the character tends to lack nuance or any real relevance to the narrative. Not to mention their behaviour is often so bizarre ... no matter how many times they get rejected they still hover around like dogs with their tails between their legs. They have no sense of pride or purpose, other than to force the lead to fall in love with them. Hehe, who does that? For me, it's soooo frustrating. They slow down the flow of the story and make what may be an otherwise alright show feel very draggy. But alas, to each their own! :-)

Shows where the narrative actually revolves around a love triangle, for eg someone caught between two lovers, work better for me even though I don't love these kind of stories (I personally prefer a definitive OTP). Anyway, here are a few recs (dramas are all Korean where otherwise stated): 

- Autumn's Concerto (TW - d) -  The presence of a 2nd lead here feels credible, but in general s/he tends to overstay their welcome. Which is another problem a lot of dramas have when it comes 2nd leads. A love rival can add good drama to a show, but they shouldn't take over the narrative to the point where they start to feel intrusive and annoying. That's in the opinion of someone who doesn't like 2nd leads; for someone like you, who is the polar opposite, this show would be great for you based on this criterion alone! Overall, I didn't really care for this drama. Personally, I thought the show wasn't very poorly put together. Everything from the soundtrack, the script, the direction, the acting ... they weren't up to par in my opinion. But I'm a filmmaker in real life so my standards for a 'good' production are probably a lot higher than most other viewers. That's why I'd still recommend that you check it out for yourself. Many, many people loved it. It's one of the most popular Taiwanese dramas on MDL.

- Love Story in Havard - the love triangle is strongest in the first half when they're at 'Havard'. This was a very basic drama for me, which means that it features all the cliched hallmarks of a Korean drama, especially those from an older school of dramas like this one, but again if a love triangle is what you're looking for then this has it. Plus you might love it even if I didn't. 

Affair themed dramas are also good for love triangles, if you can overlook the bitter taste most of them will leave in your mouth. I can't so I tend to avoid them, but these ones were tolerable: 
 
- A Good Wife (TW- d) - If Autumn's Concerto is the worse produced T-drama I've seen, A Good Wife is the best. I wasn't so jazzed about the romance, but I really enjoyed the overarching story, which explores the role of women in traditional Chinese society. How you're expected to set aside your own ambitions & needs in service of husband and family. What I loved the most about the show is that it's criticism of the oppressive conditions women are forced to live under, even in this modern age, is very subtle. It doesn't really point a finger at the individual (who are often not bad people), but at the system which created the monster, so to speak. There are no real bad guys (except one), only people who are products of the environment they were brought up in. It's really a good watch. I didn't like the romance, but that's because I was rooting for the other guy. You might like how it's done just fine, though. 

- Lovers - This is one of my all time favourite dramas in the romance genre. The story had a very real life component to it, which is why it worked for me even though there's a love triangle and emotional infidelity. Also the best thing about the show is the chemistry between the leads. It. is. EXPLOSIVE. The drama is written by the same screenwriter as A Gentleman's Dignity and the upcoming Descendants of the Sun, both of which I see are on your list. (By the way, I also rated AGD a 9! :)

Other shows with 2nd leads: 

- Que Sera Sera - This is the first drama to feature a hardcore love square that I liked. It's a show about 4 people whose lives intersect. Watching this show is reminiscent of being on a roller coaster ride. But it's not the type of ride that makes you throw up once you get off, it's the kind that makes you go 'Can we go on it again ... now?'. At least that's how it was for me and it would appear some portion of the viewership agree. Oh and Eric Munn ... hmm mmm ... he's a treat! :)

- Cunning Single Lady  - I dropped this drama, not only because of the 2nd lead, but because in general the story wasn't really to my taste. I don't really go for the goofy, nerdy type of male leads. I like the bad boys or the calm, scholarly type of males. But I'm rec-ing it to you because I don't know your taste so this drama might be right up your street. It has an attractive 2nd lead and he's quite present so it meets your requirements in that regard. This drama was also very popular among the MDL viewership when it aired. 

- Loving, Never Forgetting (C-d) - There are several reasons why I liked this drama. 1) Jerry Yan  2) I love these type of stories -- it's about this rich guy who didn't know he had a son. The drama is about him bonding with the kid and rekindling his relationship with the boy's mother. However, one thing that lessened my enjoyment of the show overall was the presence of the 2nd lead (and some of the female lead's more idiotic behaviour). haha

In most Hong Sister dramas the 2nd lead normally has a very strong presence. I see from your list that you have already watched The Greatest Love and Master's Sun so try some of their other dramas, for eg Big or the more popular My Girlfriend is Gumiho. I personally dislike the Hongs exactly for the fact that they use 2nd leads so arbitrarily in their dramas (and the romance in their shows is so childish). So I've kind of sworn off them. But for those who like 2nd leads no matter what, they're probably the best writers to follow!

The thing is I actually don't mind a good triangle when it's presented logically. Love triangles, if done right, CAN create some darn good drama, but in most Asian dramas, at least the ones that I've seen (admittedly not all that many) ... the 2nd leads are just plain silly. They're not really there to advance the plot, but to create ridiculous, unnecessary drama to fill space and to keep the main love line from advancing too fast in a less than sensible fashion. This was really very obvious in a drama like Cunning Single Lady for eg, that's why I had to drop it and if you knew me well, you'd know how much I hate to drop dramas (esp a drama with a pair of leads I really like). 

I should have dropped Autumn's Concerto too, but I couldn't bring myself to leave it unfinished so I suffered through all the madness. Yes, it is VERY melodramatic and makjang. ALL the standard cliches dramaland has to offer, you name it, it's in this drama. I was still a rookie when first watched it, but I knew immediately something wasn't right. It was waaay too over the top. But alas, I finished it and even gave it a 6, which means there were elements I liked and disliked equally. What I liked was the cute family scenes between the male & female leads and their kid, and the overall nice chemistry among them; the rest was just noise. Literally. That horrid, repetitive theme song almost drown me nuts. The only pity for you is that it does have a love triangle that I think you might have liked. It certainly was the closest I've ever come to having 2nd lead syndrome. 

Lovers was the great exception when it comes to triangles. Funny thing is that in terms of cliches, this drama is very typical K-drama, but 2 things got it right for me 1) Excellent chemistry between leads! I have not seen chemistry this good before or since and 2) the way the usual cliches are presented makes sense to the circumstances the characters find themselves in. They didn't feel totally random, whereby a 2nd is inserted into the plot just for the sake of having a 2nd. She created a story that's born organically from a love triangle. That way even though she's perhaps using all the cliches in the K-drama playbook and which we've all seen before, they seem fresher, less absurd.

As for the 'affair' aspect of the show, let me just say there are WORSE affair dramas out there, like, er ... Temptation. This drama pissed so many people off ... I don't even have words to describe it. I have a review up, if you'd like to get an idea why. Absolutely THE worse drama I have ever seen while Lovers is one of the best. They aren't even in the same ball park. Lovers may be about one character falling out of love with their long time partner and focusing their attentions on someone else, but just the WAY the situation is handled is very delicate and non-threatening. It's sensitive to the point of view of all involved. I never felt bad about the leads being together, I rooted for them all the way. I can absolutely not say the same for Temptation,,  that wretched drama that made me want to turn into a violent person, because, yes, if I had a shotgun, I'd blow these characters away. LOL That's how BAD it was. I strongly recommend that you do not watch this drama,  if you're a romantic, sensitive soul. 

I loved Reply 1997! And yes, the love triangle between Shi Won, Yoon Je and Jun Hee was not too bad ... maybe because I saw it as more of a beautiful friendship with the lines temporarily blurred for one party as opposed to it being a typical triangle -- the one that's just there to cause aggravation and frustration.

Based on how you described why love triangles work for you, you have got to give Que Sera Sera a try! I have a feeling It's right up your street.
I hope you find something that you like! :)