I'm pretty sure there are royalties for DC & Marvel artists these days, going back to the big squall in the 1980's. (For when their work is recreated, not their characters. They give the characters over 100%.)
This doesn't mean that Disney should or should not follow that practice.
If by "work for hire" you mean the company owns the work, I agree completely. But they also, by contract, give royalties when issues (including reprints) sell over a certain amount. (You could also say that their base pay for the work assumes a certain number of sales.)
This doesn't mean that Disney should or should not follow that practice.