There's more to developer experience than that. Your comment even demonstrates one of the differences: The .NET library compared to a bunch of different Java frameworks.

That is indeed a technical difference. But I don’t see much significance in it.

Spring is a de-facto extension of the core java libraries and alternatives like Quarkus follow the same mental model with a better technological foundation.

Maybe, but with all the modern .NET tooling I feel at least 2x productive in .NET than in Spring Boot. There are a lot of quality of life stuff in .NET/C# that really does add up and makes a substantial difference (DX-wise) in the long run.

The culture around Java and C# are very different. I'm not sure I can explain it.

I could continue to point hundreds of technical differences but that's the trees and not the forest.