Both deal with time travel/romance. Both FLs sort of "messed up" in their current life and both plots revolve around the FL changing herself to give herself a better fate

Both have respective son/daughter traveling back to the past to meet their parent. Very cute and heartwarming child/mother bond is formed. Both also have some cute romance side stories as well!

Both are female centric dramas, although To Dear Myself is a lot heavier on the heart/they take a more realistic and less idealized viewpoint on life.

Both have detective work and are fairly fluffy romance dramas. both dramas focus on the romance aspect of things and are rather light.

Both have detective work and romance. I would say Under the Power is more focused on the detective work whereas Maiden Holmes is more fluffy and focuses more on the romance. Both are very good shows!