I would argue that mature frameworks like Rails or Django are peak productivity though - but, by all means, throw in a front-end framework like React to fill in

I would argue that mature frameworks like Rails or Django are peak productivity though - but, by all means, throw in a front-end framework like React to fill in the gaps if you need it. I personally don't think the performance trade off is worth it. And it drastically increases front-end complexity in terms of state managment, which you now have to also manage in the client. The complexity is just moved further away from the server and productivity is gained on the visual part but lost everywhere else.