After a naive removal of the tests (every folder and files that contains tests was deleted), React still has 190k lines of code.

> React has one job, and it does it really well

I'm not sure I agree. It's hard to compare without a minimal copy of React to see how small it can get, but I'm guessing it could be an order of magnitude smaller. For example, React supports different ways of doing things (class components, function compenents, hooks). Backwards compatibility is a great thing, but it's not the same as "having one job and doing it well", it's a different tradeoff. The React team has lots of people that depends on their code, and thus choose stability over being small and nimble. I think that's a responsible choice. But this leads to complexity, and losing the "having one job and doing it well".

As a more general remark, there's a cycle in software. React starts small and nimble, especially compared to the "jQuery behemots of the past". It gets really popular. So people start depending on it. So it grows, and grows, and grows. And then someone else comes out, maybe Photon, maybe Svelte, maybe something else. Compared to React, it's small and nimble. Maybe in 10 years, Photon will be really popular, will be 200k lines of code, and someone will build an alternative because it's too big and complex.

Edit: as a more meta-remark: My message is way longer than yours because I was trying to steelman my argument, and you didn't do the same with yours. Considering you made a small message "defending" React and I did a long one "defending" Photon, I think we already agree about the tradeoffs involved here.