I think the Marvel downfall talk has been premature. Obviously they have underperformed over the last few years. But I’ve always said the tale will be told with the next few films:
Spider-Man
2 Avengers films
Black Panther
X-Men reboot.
All franchises with a track record of success and maximum public knowledge.
If these films underperform or if only like one does well then I’ll start thinking that it may be over. But it’s about rebuilding trust with the audience and if they’re all good to great films then Marvel is due for a renaissance.