More than just romance, both have age-gap-related matters and thought-provoking issues around life and family.

Both are detective dramas, have small connected crimes inside a big dark scheme. Both have slight romance and a tragic ending for the romance. Luoyang's plot is somewhat more braintwisting and enthralling than the other, but the details of the crimes are equally fine.

Both have a very meaningful message towards humanity and well structured plots. The two come with detective activities and have surprising hidden villains.
But TLLTM has a much better ending, though at first its pace is not as suspenseful and fast as Luoyang. It also focuses more on the romance side compared to Luoyang.

Both has detective factors as one of the main point. The plots are well structured and some eps are quite suspenseful. Both have great MLs with phenomenal acting. FLs in these also bear great heroine characteristics, i.e. strong-minded, witty smart, good-natured, and soft-hearted.
While Under the Power has much brighter mood and ending, Luoyang is unmatched in some other aspects and also humanistically meaningful.

Both have the beautiful annotation of death, deep listening, experimental moral, and living life fully no matter what.