Biggest one is lack of null-safety. The preference for implicit value defaults, sketchy error-handling, and similar choices also rub me the wrong way. The whole thing just feels too fast-and-loose for my tastes

I'm the thousandth person to suggest this, but my ideal language for web servers and lots of other things would be Rust with a GC instead of a borrow-checker. But Rust has its unique killer-feature to thank for a lot of the traction it's gotten, so it's very possible this hypothetical language never would have taken off in the first place. We've got what we've got, languages are social constructs just as much as technical ones, maybe even more so

Kotlin and Scala exist

Kotlin still has the annoying points of any jvm lang. Gradle, weird ORM stuff etc.

C# exists