I believe the Model View Controller or Model Template View architectures provide sufficient separation of concerns without requiring separate codebases, teams, tooling, and project management.
A proper FE developer who knows about accessibility (not just ARIA-attributes but also contrast and usability), UX, semantics, and also being capable of delivering performant user interfaces is rare these days, because people think full-stack development really is a thing. I think it is one of those mythical things like a 1000x engineer. People think that they can get away with 90s style websites, but please test stuff with a screen-reader, and also while you're there get some front-end consulting, you will be surprised how badly you may be doing. IMHO, many need dedicated FE development. Whether they use React or not, I think many do. You can distribute many responsibilities on non-technical members of the team, but then you start thinking "couldn't they just learn a bit templating so I don't invest so much time on implementing their seemingly never-ending requirements"!
BTW, this separation is of course also possible with your traditional MVC stack, which I also use in my personal projects a lot, in which React is indeed overkill, and there are many cases that a bunch of templates deliver all the things you may ever need. If it gets complicated enough some day, return your View Model as JSON and there you have a perfect API. IMHO REST APIs aren't suitable for any dynamic front-end development anyway.
The only reason I wrote that single sentence in my previous original comment is that React forces your hand a bit, in this matter. It's a small point among other things.
It also doesn't end there. There's the UX part, re-usability (huge difference to have a cross-team front-end service-team), performance (not just initial load... Are the widgets you build with, say, Alpine.js tested for performance?), development speed, caching, offline-capabilities, opportunistic rendering, other best practices, branding, consistent design and interaction and so on. It's a science on its own.
Front-end is not just some basic thing which got a complex solution for no reason. It is a complicated task.