Analysis of information sources in references of the Wikipedia article "Browser extension" in English language version.
Nobody outside of Google really has any meaningful sway, since Chrome currently owns nearly all of the market share; Google sets the rules, other people nitpick minor details, and everyone pretends that everyone had a meaningful say.
Google has shown no interest whatsoever in deviating from their original plans. So, it's quite clear what's happening here. MV3 is a business decision, not an engineering decision.