I think it's a huge loss. Generic type erasure is the main thing that makes simple polyglot interop and code-reuse on the JVM possible. Even things like Python become clunky on .NET because of runtime generics. I gladly give up on the tiny usability gain in exchange for having a rich language ecosystem.

Value types are a different matter, and they are now being added to Java as well. Specialized generics over value types are different from specialized generics for reference types, because they are always invariant.