Yes and no. Systems with fundamental problems should be redesigned from the ground up or reverted to previously successful iterations when it's appropriate, but features that already work very well shouldn't be completely scrapped just for the sake of trying to make something a little bit better.
Class design from MoP to Legion features a lot of examples of polished systems being torn up and rebuilt, and the abandonment of the justice/valour system led to all sorts of problems with the reward structure in WoD's end game, followed by the slow reintroduction of PvE currencies in less elegant forms.
Now that I think about it, most of the design problems with WoW feel like they stem from this stuff. Either large problems are slowly iterated upon when sweeping changes would probably work better, or small issues face anthill-nuking solutions instead of careful tweaks. Overall I think slow iteration is probably better, though. Veering off course can be corrected when the changes are small, but it takes a long time to climb back up when you blindly drive yourself off a cliff.