The cards themselves have to be powered down as a result, which can often lead to less interesting designs
The reason it sees so much play is that it is doing two things that are well paired, both stalling the game and it is never a dead or even that weak of a card in any given matchup
Get rid of stuff that goes over your head and keep your board
These are easy combos to include in the Undead Unleashed deck, while at the same time, letting Mikaeus also serve as protection for Wilhelt, the Rotcleaver and other non-Human creatures
Amano's planeswalker, Liliana, is also one of the central figures in War of the Spark's story, and will likely be a key player in the game's new Standard format thanks to her extremely high power level
I would then look to cut either Liliana or Courser depending on which colour was getting toned down