For my tastes, this is a massive blow to the future of the MCU. Spider-man should have been the "new Iron Man" in that he would appear in all kinds of movies and be an adhesive that helps us care about the movies of obscure/new characters.
If they don't fix this and get him back in, I'm ready to declare this moment as "the beginning of the end" for the MCU. Don't get me wrong, it will take a long time for the MCU films to wind down performance-wise for them to stop making movies or reboot the universe. But with X-Men and Fantastic Four not ready to release movies for a good while, I suspect too much momentum will be lost and history will look back on Endgame as the peak of the MCU, after which it began a slow decline. Possibly a decline with a few peaks, but nothing that ever reaches the heights of Endgame again.
Other perspectives and predictions?