The standalone films continue doing generally bigger and bigger box office by comparison. The Avengers films absolutely should be outperforming the others.I think the bigger issue for the MCU going forward is that most of the characters on which that success was built are either already gone or will be soon.
There's no guarantee that the new characters they introduce will draw people in the same way -- the standalone MCU films have already generally performed at much lower levels than the mega tentpole Avengers films while still starring part of that established main cast. There's a chance no one is going to really care about films like The Eternals.
Of course they still have at least one more film for the Guardians, Thor, Spider-Man, etc. which should carry them forward for a few more years even if newly introduced characters don't do well. They also have the ability to try the Fantastic Four yet again and, more importantly, the X-Men. They will probably be just fine.