Name one that gives 100% parity to React in their SDK to write extensions.
Not works in some of the cases and you have to implement fetch calls yourself, or some iframe boilerplate and JS glue, everything they expose in React is fully available in Angular, including field extensions, inline previews, sidebar extensions, the whole lot.
That doesn't change the fact that there is a lot of Angular out there. No one's doubting how useful Next.js may or may not be, it's just a matter of fact that plenty of systems were created before it was available and not everyone has the luxury of rewriting their entire product.
I'll be honest I have never heard of this nor do I understand why it matters. It looks like it's just internal Vercel marketing speak that basically amounts to them desperately trying to build a platform and extract rents off of it.
It matters, because React is one of the reasons FE development sucks nowadays, and in many cases there are no alternatives, unless one loves yak shaving for their framework du jour.
Not works in some of the cases and you have to implement fetch calls yourself, or some iframe boilerplate and JS glue, everything they expose in React is fully available in Angular, including field extensions, inline previews, sidebar extensions, the whole lot.