5% costume buff for the original challenge event heroes makes sense to me. They’re fairly aligned with season 1 heroes.
However, the universal buff is undeserved because costumes are being added for heroes who are already good without their costumes (i.e. Black Knight, LOTL).
Overall this won’t change much. I do appreciate a change to “base” stats rather than just focusing on specials. I view it as a net neutral.
This will cause some confusion among the player base. We already get relatively regular posts about costumes bonuses.