Speaking from brief television experience, it's not screenwriters overcorrecting, it's execs and producers saying "we like this character, rewrite it so they're in it more" or "make that character funnier", or even "I like ice, can we set the climax somewhere where there's ice", and after rewrite after rewrite the writer loses perspective and forgets to think properly about what he/she is writing and whether or not it all fits together.

This particularly happens when producers/directors start forcing rewrites of the script while the film is shooting, or even going back six months later for a whole range of re-shoots - which is apparently something that happened with Wolverine.