Isn't next.js too big to fail? Currently we are trying to define a modern stack for our front-end, and I always thought next.js/react to be the next java -> Perhaps Solid.js is much better (IMHO it surely is) but I probably won't get fired for choosing next.

There is a huge amount of difference.

Java is currently backed by Oracle, which has a huge history of staying around (setting the reputation aside for a moment).

Vercel is currently not profitable, raised too much money and is stuck trying to generate enough profit to match that valuation.

Also NextJs is relatively small in the world you compare to.

Javascript <-> Java React <-> NextJs <->

i.e. it sits another 2 layers below.