Apparently, the delays did help improve Brave New World. Based on early test screenings and comments from people who saw those initial cuts, the finished film is reportedly a much better film than what was originally shown. Even if the end result now is considered just “okay,” or “serviceable”. It sounds like the earlier version was significantly worse, so there was clearly room for improvement, and it seems they made the most of that. Even though the movie could have been much better imo.
As for Shang-Chi 2, I’m confident we’ll get it, but it’ll likely come after Secret Wars. Having Shang-Chi appear in Avengers: Doomsday and Secret Wars should give his character a big boost, more exposure and excitement with general audiences before diving into his sequel. That could play a big factor, into building momentum for his second film.
I also think the delays benefits the Russos. They haven’t missed when it comes to comic book movies. Every one they’ve done has landed extremely well, from Winter Soldier to Endgame. With more time to work on Doomsday, I feel confident they’ll deliver at least a really good movie. Just how good it’ll be, we’ll have to see, but with the Russos returning, one of the original writers back, and everything I’ve heard so far, I believe they know what they’re doing. I'd bet money that it’s much better than Avengers Age Of Ultron, and is closer in quality to the catalog of the Russo brothers previous work.