I think what the past few years shows is how big losing China & to some extent Russia have been to Marvel's box office (Russia is actually a lot bigger of a deal for Avatar than Marvel). Obviously studios are simply choosing not to release themselves in Russia because of the ongoing War in Ukraine, so that's a bit different than China. However, the original movie made over $100M in China and close to $19M in Russia, so while even matching those totals wouldn't have put Wakanda Forever over the $1B mark, China sure as hell would have put Multiverse of Madness over the top.
There's actually several $1B grossers in the MCU that wouldn't have made it over the hump without China. Captain Marvel made $1.129B and $153.8M was from China. Civil War made $1.151B and $180.8M was from China. Far From Home made $1.131B and $205.4M came from China. Even Age of Ultron, while it would still be a billion dollar earner, it would've only made around what Civil War made as it made $240.1M in China and would've "only" made around 1.154B.
The main point is, the MCU either has to figure out how to live without China or get back in. Infinity War made $359.5M and Endgame made $629.1M in China. which is almost $1B alone between the two movies. I'm sure Disney would hate to miss out on that kind of money for Kang Dynasty and Secret Wars, but at the same time, would audiences still show up? The MCU that Chinese audiences knew has changed so much in only a few years.
Let's also make no mistake... movies that gross between $750-$950M are no flop. That proves public interest. But much like Avatar 2, there's the case of being successful with the public versus financially successful, which is still fluid for that movie. I'm not sure Thor 4 actually got into the black (the budget for that movie was huge for some reason). Wakanda Forever and Multiverse of Madness are fine.