Both Elixir Phoenix and Ruby on Rails use plain HTML by default but they both support view morphing (phoenix via LiveView and rails via Hotwire Turbo). It really doesn't cost anything to add it. Clicking links with a bit of caching can make it feel near instant the way a (small) SPA does. Adding link prefetching algo on top of the that and it will seem even faster.

If anything it removes a ton of the argument for using React absent maybe a small subset of highly complex UI subcomponents which may need it, but rarely required for a whole SaaS app. Frontend teams just want React so they can use a single tool not because it's the best solution.