Both are dramas which have the ML centered on revenge. Both MLs become rebels against the King. Both constantly get separated from their love interests, but make their way back together in the end.

It might sound strange to compare a drama set in modern times with a historical drama, but honestly, if the setting doesn't bother you, then you might find these two dramas eerily similar.

-Both have ML's set on revenge against the FL's father.

-In both dramas, the MLs is first seen as light-hearted and charming, yet as the drama progresses, both ML become more serious and gloomier. Because of their darker disposition, both MLs push their love interests away.

-Both FL's are immature in the beginning (however, in Prosecutor Princess, it is more apparent). but they mature as the plot progresses.

-Park Shi Hoo is the ML for both dramas

There are plenty more similarities, but if I mentioned them, they would spoil the story too much.

-Both produced by Daylight Entertainment, so they give off similar vibes
-Both FLs are the analytical type.
-Both Detective dramas
-Both have less romance, more action

Similarities:
-Same type of female lead (cute and dumb)
-Both Female leads have an unrequited love for the Male lead at first
-Both Male leads are standoffish and highly intelligent and become doctors.
-Both SMLs blindly chase after the FLs despite the FL not liking them back.
Differences:
-ML in ALSB is less of a jerk. (but still a jerk nonetheless)
-More fluff moments in ALSB
-SLS is a little more stronger in ALSB
-ML is more friendlier in ALSB

They have the same overall vibe. I'm not sure why exactly, but FTLY kept reminding me of PK while I was watching it. They're both light romcoms and both use cliche tropes.

-Both female leads have very similar personalities, and looks

-Both male leads have a goal which is the reason they try to hold back from falling in love with the female leads.

-Both male leads are the female leads' boss

-Both are Taiwanese

-Actors/Actresses in both dramas are very good-looking