Remodel is a pretty good reactionary card, however it's still reactionary.
Its more effective to use the witch than to deal with the witch.
In order to Remodel the Curses (into Estates or whatever), you have to get a Remodel, potentially wasting a buy, get lucky and have a hand with Remodel and a Curse, and then waste an action Remodeling a harmful card into a "dead" card.
It's strictly an improvement, yes, but it's better to force that on opponents than have to do it yourself.
But either way, you are either playing the card or reacting to it. It forces particular strategies more than I would like. (And more than most other cards.)
Likewise with Chapel, one of the only ways to screw over the Chapel strategy is by using lots of theives.
(Chapel strategy being: get a fair amount of gold, chapel away everything that isn't gold or provinces. You end up with a small deck that can buy a Province every turn.)