In the most recent "From the beginning to the Endgame" trailer, Marvel used Iron Man, Thor, Captain America, Avengers, Guardians of the Galaxy, Ant-Man, Doctor Strange, Spider-Man, Black Panther, Captain Marvel, and Infinity War as the key franchises. They did not use footage from TIH, TWS, AoU, SM:H, or GotGv2. So I would argue those are the skip-able movies. And when you break it down, they really are.