other efforts to make an independent web engine such as Ladybird.
Notice the word efforts here. No one has actually succeeded yet despite multiple attempts, some even by Mozilla themselves like Servo. Ladybird is not a fully functioning browser yet. Are they anywhere even close yet? Even if they are close it also has to be fast. Google and Mozilla have spent quite a bit of time, money, and effort making their JavaScript engines as fast as possible.
I will have a look at some of the links you have given, but honestly I think most criticism thrown at Mozilla isn’t anything close to what the alternatives are guilty of, and is mostly done by conspiracy nuts. The kind of people were Mastodon and Lemmy is their only social media, and refuse to own a modern smartphone that isn’t running custom firmware.