Are they standalone though?
In Winter Soldier, the reveal that SHIELD is HYDRA only works if you go into the movie knowing that Hydra=Nazis who Cap beat up in the war before going under the ice. You really need to have seen Captain America First Avenger to understand the emotional thrust of that. Likewise, Bucky=Winter Soldier. Also Arnim Zola aka the mousy sidekick of Hugo Weaving's character is actually some advanced computer program. I mean that's on the level of needing to have seen Captain America 1 to see Captain America 2 so it's not a big deal as say Captain America Civil War (which makes no sense if you haven't seen Avengers 1, Winter Soldier AND Age of Ultron on top of that).
Captain Marvel assumes a lot of broad knowledge on the part of the viewer, namely about Nick Fury, the Tesseract (the source of Carol's powers whose mechanics aren't explained fully in the movie and you need to know from earlier movies that the Teserract is some weird McGuffin), and also Ronan the Accuser.
Guardians of the Galaxy and Black Panther are
relatively standalone, I'll grant you. I mean yeah Thanos in Guardians being our first impression of the great villain of the series but even if you didn't see the Avengers you sort of know from the movie who and what Thanos is/supposed to mean. Black Panther likewise.
But even then on a stylistic level, all these movies look pretty samey. This video by Patrick Willems talks about this. and in all likelihood when Scorsese is saying these movies aren't cinema, this is what he's probably referring to.
He has a three part video on this if you want to check it out for a longer argument. Here's part 1 where he expands on that (
https://www.youtube.com/watch?v=u6Bq_jK0Z1Y).