There are some movies that don’t need any help and there are some that are beyond help. Despite that, I think there are some actors who always make a movie better than it would have been. They aren’t always leads, but any scene they’re in is worth watching. My list would start with: JK Simmons Rachel McAdams Michael B Jordan Tilda Swinton Jeff Daniels Ming-Na Wen
Who are the actors you feel the same way about? Or do you disagree with the premise?
Eugene Levy. Much of his career as an “ensemble man” where he constantly stole the show. He nails every line, intonation, and timing in ever scene in every movie or show he’s ever done. Rembrant of comedy.
Keanu Reeves. Not because his movies, scripts, plots, co-stars have all been aces, but because, per your premise, he adds to each of his movies, and some of them he doesn’t necessarily define. Someone with the range to play in Branach’s Much Ado about Nothing as well as Bill and Ted’s excellent adventure.
Bill fucking Murray. So many of those flix could have been horrid but he made them classics, Stripes is a good example, if you take him out it’s a zero.
As much as I love Keanu, I’ve seen some films which he made a bit worse IMO - like Dracula. Bill Murray though - yep.