Recommendations

A similar sweetness between the romance parts of those two dramas , and very appealing characters in both shows. However, Strong woman has more suspense and dramatic moments , but still very funny and cute parts like in Weightlifting fairy.

Mainly because It has the gorgeous Oh Ji Ho, a dimpled, handsome lead just like in Who's the one, and he's hysterical and sweet as Overweight Karl before he transforms himself into a lean, gorgeous Pro-Golfer. And it has the talented Uhm Jung Hwa as his leading lady upending his life once again.

In both dramas the two main male leads (also childhood friends) are fighting over a female in a rich-poor society circumstances.

Similar plot. Kind-hearted woman saves elderly man, who then decides she deserves his entire fortune. Arrogant grandson wants fortune and after hijenks falls in love with woman.

The plot here also revolves around the act of revenge and also possesses similarities.

If you watched the Lost Tomb (parent story), then I would also recommend the movie version. Also for those who like to watch movies more.

Both are action movies focusing on undercover cops trying to take down crime organizations.

KIM SEULGI! To be honest, nothing common for the plot line except that they are short drama/specials. But if you like Kim Seul GI's sass and cuteness you will definitely enjoy this two drama. Her chemistry with all the actors is like omg omg omg. give her a full drama pls (better with doo joon)

Both dramas are directed and written by the same director/writers and Deep Rooted Tree serves as a direct sequel to Six Flying Dragons.
It follows the story of King Sejong who is Lee Bang Won (King Taejong)'s son (he appears in the last episode of SFD).
Since the two dramas are written by the same writers, many characters are interrelated such as Moohyul and Lee Bangji who are actually made up characters. Also, Mokya, Parkpo, etc. who are supporting characters in Deep Rooted Tree made special appearances in the last episode of SFD.
I highly recommend watching DRT where you can see the older and the more mature Moosa Moohyul.
It's really heart-warming to see recurring characters and you'll end up missing SFD but then again, you'll fall in love with the new ones from DRT.
P.S. Although Shin Sekyung appears in DRT, she takes on the role of a different character :)

Both are about prodigies in surgery & an outstanding doctors.
The main character is also impudent if thats what it takes for a sake of the patients.

Both male protagonist have a cool demeanour, is fighting for something (a goal to reach). Both dramas have cool "agent" scenes and a female protagonist that fall in love with the male protagonist.

Both movies are about families that have to deal with the aftermath of a brutal crime that has been done to their daughters.
Both fathers show the extent of what they are willing to do for their daughter.
Both are brutal, tear jerking movies.

Both movies have the same actress for the female Lead, both deal about a romance story where one of the pair has to deal with a disability/condition.
Always is more dramatic than The Beauty Inside.

Both have male leads that belong to a different time period and in love with someone from their own time periods. In both, male lead is taken care of by modern day female lead, who was either reincarnated or similar to someone that male lead knew about in his time.

both deal with ghosts, both have a similar atmosphere, both have a fun humor