Let’s say you think it’s not React or you have time to improve React to solve that problem: wouldn’t having some data help test that assertion and make changes?

We have the data: they removed React and performance increased by 50%.

Why should any more work be put into keeping React or improving it if their solution of removing it entirely already works?

Well, for one, cause they did /not/ remove it entirely: They use it on the server.

It doesn't "work", it's a hack.

50% isn't data. It's a claim without evidence. The evidence in this case may help fix React.