The game tree is both broader and deeper in Slay, so much harder to do tree search. Also very irregular; in chess you have very few situational decisions (eg en passant, castling) whereas many decisions in Slay are one-off (events) that are quite hard to weigh the EV. Finally you don’t have perfect information in Slay, which makes things WAY harder.

You’d probably want to look at Go AI instead of Chess, but better would be the Dota / StarCraft AIs. Very different architecture.