So I'm looking for a school / workplace, slice of life that has multiple characters that it develops. The problem I'm running into is I'm finding dramas that all center around one specific inspirational main character (like a teacher), OR it ends up being a romance where everyone except the 2 main characters are supporting cast and have little to no character development (pls no more romance just friendship lol)

I'm actually noticing a trend where japanese dramas usually focus on one or two quirky individual main characters, and all the side characters are put into tropes. I liked a couple kdramas because they developed their side characters a lot, and emphasized the fact that people aren't all stereotypical tropes like the "bad boy" or the "nerdy girl". They had their own experiences and pasts that gave them a lot more depth and made them much more realistic and relatable.

Anyway yeah my title wasn't exaggerating, it's a very specific type of thing I'm looking for. But if you know any show along these lines just gimme a suggestion, doesn't have to be school or workplace, or Japanese. I was hoping to find a jdrama along these lines because I'm trying to learn Japanese, but I can always just look for another kdrama or American TV show like Glee lol

EDIT : Thanks for all your suggestions! I've already started watching Omotesando Koukou Gasshoubu and it's really good. It's pretty relatable, and I can already tell there's going to be a lot of depth so many of the characters. Best of all it focuses on a hobby like choir, rather than just romance. Also bookmarked Age of Youth, HERO, Hanazakari no Kimitachi e, and maybe Tumbling if I can really get interested in the sport it focuses on. Toss me some other recommendations if you can!
The first one I thought of was Omotesando Koukou Gasshoubu. There is one main character but generally, every episode is about one student or teacher and their very own story. There is a tiny bit of romance, but it's never the focus. But this may also fall into the "one inspirational main character" trope that you mentioned, since the main character usually helps the others out. And maybe Love Shuffle. This is a romance drama, but there are multiple main characters that all stay equally important throughout the whole thing. And friendship is just as, if not more important. Every characters story is very well developed. 

Sorry, I can't really think of anything that fits all of your criteria.
Oh and you should definitely check out the kdrama Age of Youth
As your list is empty, I might probably name dramas you've already seen. 

First school drama that comes to my mind is Nouta wo Produce, there are three main characters though
You can also try the following ones. As Omotesando Koukou Gasshoubu already mentioned, some of those school dramas are focusing on a different character each episode :
- Gokusen
- Akihabara@deep
- Aogeba toutoshi
- ashita, mama ga inai (ot really a school drama)
- Dragon Zakura
- Gakkou no kaidan
- Hana Yori Dango (maybe too focused on the main couple though)
- Hanazakari no Kimitachi e aka Hanakimi, this one is highly recommended.
- Honey and Clover
- LIFE
- Long love letter
- Nodame Cantabile
- Orange Days
- Ouran High School Host club (but we can't say characters are well developped)
- Stand up!
- strawberry on the shortcake
- Suzuki sensei
- Taiyo to umi no kyoshitsu (highly recommended)
- Tumbling (highly recommended too, many characters well developped)
- Water boys
- Yamada-kun to 7nin no majo
- Yowakutemo katemasu
- Yukan Club

Some workplace dramas :
- Aquarium girl / other dramas
- Boss (i don't remember well though)
- Brother beat
- code blue
- Doctor's affairs
- Hayako sensei -(focused on love stories of 4 colleagues)
-  Hero (highly highly recommended + Kimura Takuya)
- Juhan Shuttai!
- Kazoku Game (all the members of the family are well portrayed)
- Kisarazu Cat's eye
- Kokoro ga Pokitto ne
- Lost Days
- Love that makes you cry
- Kiseki no hito (miracle man)
- Miss Pilot
- Namonaki Doku, and above it it's second season Peter no Souretsu
- Nankyoku Tairiku (highly recommended too, many characters)
- Shitsuren Chocolatier
- Summer Nude
- Sunao ni narenakute
- Wakamono tachi
- Yamato Nadeshiko Shichi Henge

Given the fact that japanese dramas are shorter in terms of episodes and episode length, you cannot expect the side characters to be as well developped as in korean dramas. Nevertheless, those mentionned above give places to the side characters so that you can enjoy them (hopefully). I've seen some of them long time ago and might not remember well about side characters.
Some specials like Mou Yuukain Nante Shinai have a lot of characters, but you can't expect them to be very developped as well.


As for korean dramas, A gentleman's dignity is the only one i've seen that dispatch the screen time between the different characters/couples.
Have you considered asadoras? With an average of 156 episodes (each episode is only 15 minutes) people often dismiss them, but one of my favourite dramas ever is an asadora and I wish more people would give them a chance. They do tend to focus on one main character, but such a long run allows even the most minor characters to get their own complex storyline and lots of episodes devoted just to them. If you love slice of life I think this genre will really be perfect for you since 156 episodes allows lots of time for focus on daily life. I've see Amachan and Mare (and would recommend either 100%), but there have been nearly 100 different asadoras so I'm sure you'll be able to find one that fits exactly what you're looking for! 
Yiu can try:

Tumbling
Rookies
Ohh I definitely second asadoras! I've only seen Mare but it's so good! There is romance but it never takes over the plot.
I know you are mainly looking for jdramas but I would recommend the kdrama Misaeng (Incomplete Life)