Honestly, as a fan of both series, Scarlet Devil Mansion would win this one. However, I thought It would be one-sided until I got more info about Spooky's Mansion feat. in the Doll House DLC, Spooky has the hell gate which can doom the whole world when the mansion explodes if it doesn't close as it will tear the boundary between the two worlds, and let the eldritch energy roam freely, Although, Touhou setting is still high for them to win against Scarlet Devil Mansion as it would be Mid Diff at most

Spooky's Jump Scare Mansion by Akuma Kira/Lag Studios

Touhou Project by ZUN