The main reason many people abandoned Firefox was because everything about Chrome was faster and more responsive. Render engine performance matters more than implementing APIs that one or two websites may ever use for anything other than browser fingerprinting. Servo was abandoned by Mozilla but the improvements to the browser engine that did make it into Firefox have sped up the browser significantly. They were the reason for a whole bunch of "check out Firefox it's fast again" posts all across the internet.
I care more about my browser being fast than I do about it supporting WebMIDI or WebSerial and I think most users agree with that. Performance and efficiency are also the reason (as far as I can tell) that macOS users stick with Safari.
I just wrote a long post about web platform & balance of power. And this is like 3000% more the real feels of the situation.
I really really hope it pans out & delivers. But it properly & rightly should be an ever shrinking piece of the puzzle. It underpins it all & flexility here would be key, better tech (parallelizable!) very empowering, put to the sword many criticisms, but yeah: it's an ever shrinking factor versus what we can do with the web.
And there are so so so few powers helping us make what we can do with the web better. Even the historic pro-web folk are trying to end the web as we know it. The "Towards a Modern Web Stack" Hixie mentality (Flutter CanvasKit) is to basically ignore destroy & end the contemporary web & html & make the browser a native app delivery platform with zero user-agency, to make it a giant moving picture show. The rest of the browsers have adopted a highly adversarial stance where every possible feature is portrayed as a threat to users, as ruin. There's just so few visionary hopeful excited people left building browsers that do stuff for people. You are so right on.
However there are still quite a lot of much, mich easier wins Mozilla has either ignored for 20 years or actively walked back on.