One semi-objective thing we lost was accessibility. Much of the site is impossible to navigate via keyboard due to naively re-implemented behavior like links being divs with click event listeners. It's actually somewhat worrying - when regulations hit us, we'll have to scramble hard to get back what we threw out.
But all in all I kind of agree with you that it's very hard to find high profile examples of sites that are "HTML first". I believe in it, but haven't actually seen it pan out. But I suspect the reasons for it not panning out might be purely in education. By the time HTML became powerful, frontend dev education was already deeply framework-focused.
