C# has value types, stackalloc, simpler FFI and a rich SIMD API, offering far better control for low-level code than Java. I don't feel green threads is a system level concern, and while Java's ecosystem is huge, it's also very enterprisey. Also, I'd disagree with more open, C# is under a more permissive license and Oracle has actually been litigious over Java.
It was notable enough to be mentioned in their release notes for iOS 17.5, https://support.apple.com/en-gb/HT214101. I think that if they have to patch it, it's serious enough to reward the researcher for it. Like, it's not charity, it's not a thank you, it's an investment in their own platform's security. By not paying out they are only hurting themselves.