The fact that I have been able to build a multi-user collaborative editor experience without a single additional dependency is incredible. I previously worked for a well-established and well-funded React team who had this feature on their roadmap for half a decade but still find it too daunting to implement.
Phoenix was a great reminder that a lot of the "frontend engineering" we find ourselves doing as React developers just isn't necessary with the right backend. It's HORRIFIC to look back at all the yakshaving I've done in my career already. Wrangling types (GraphQL, codegen libraries), wrangling queries and data-fetching (react-query, SWR, server components), fiddling with middleware (serverless functions, getStaticProps, CDNs). I've seen teams outright abandon testing because the hours they invested just weren't catching any of the bugs that mattered.
I'm not doing any of that anymore. I'm spending that time refining the core data model, improving test coverage, thinking about go-to-market and making money.
Phoenix may not be a good choice if your product has reached that level of maturity and product-market fit where you really should care about "microinteractions", fine-tuned animations, or advanced use-cases for an SPA like offline support and highly-optimistic UI. But I would argue that even mature products don't truly need these things. Just look at the GitHub UI. I've spent a truly astronomical number of hours in that UI and never wished I had WYSIWYG text editing, or animated skeleton UIs, or the dozen other things that the React community tells us we need.