The washed out grey thing was an error that became a style!
Because HDR wasn’t natively supported on most displays and software, for a long time it was just “hacked in there” by squashing the larger dynamic range into a smaller one using a mathematical transform, usually a log function. When viewed without the inverse transform this looks horribly grey and unsaturated.
Directors and editors would see this aesthetic day in, day out, with the final color grade applied only after a long review process.
Some of them got used to it and even liking it, and now here we are: horribly washed out movies made to look like that on purpose.
The transition from Avengers to the later movies is very noticeable, and one of the worst offenders since source material really speaks against the choice.
What you said, it's definitely become a style. But, also, a lot of these movies that look like ass on Joe Public's OOGLAMG $130 85" Black Friday TV in his brightly-lit living room actually look awesome if your entire setup is proper, real HDR devices and software, your screen has proper OLED or local dimming, is calibrated to within an inch of its life etc, and you view them in a dark home theater.