You started that off by raising an interesting point. Pity you had to ruin it by telling us you're exceptionally thoughtful and profound, and that those who disagree, suck!
It's true, the amount of work that would be needed nowadays has made the idea of building a new browser engine almost impossible (I don't know how the Ladybird devs are getting on). It's a reason to encourage people to support Firefox on desktop, since just about everything else is based on the other browser engine. I still miss Opera's Presto - we don't want to lose another one, or there'll be no competition at all.
But as we've already crossed that threshold where the workload is preventing new engines from being built: choosing not to use new features, after they've been added to all the existing browser engines, isn't going to help that situation in any way.