People, including those who gave us Java's generics, have always argued that erasure is a problem. It wasn't something that was desired, but rather a necessary evil for easier backwards compatibility.
As I understand, it turned out to be also useful for more than backwards compatibility (though that was entirely the reason for it) -- its why you could have Scala which its richer type system and a good interop story with Java, whereas the attempt to provide the same thing on .NET faltered in large part because of the .NET platforms reification of generics.
It was never about "backwards compatibility". It was always entirely possible to introduce generics and still have both the compiler and the runtime perfectly backwards compatible. C# did this going from version 1 to 2 of the CLR. You can still run any bytecode compiled for version 1 on the version 4 of the runtime to this day.
No, the issue was a much more esoteric one (and an invented and self-inflicted constraint by the designers themselves) of migration compatibility. Consider entity A using compiled libraries (no source available) from vendor R and from vendor S in the same product. Vendor R releases a new version of his library and uses the fancy new generic collections - and refuses to maintain a non-generic version. Vendor S releases a new version of his library but refuses to provide a version that use generic collections. Library S calls code in library R. All of these need to be in place to require migration compatibility.
> its why you could have Scala which its richer type system and a good interop story with Java, whereas the attempt to provide the same thing on .NET faltered in large part because of the .NET platforms reification of generics.
Do you have a source for this? In my view it is the opposite: Reification is the right solution as it makes reified types part of the first-class system with no strange corner cases. It is type erasure that treats realized generic types as second-class citizens, with strange constraints bubbling up through the entire system.
There's a lot of second-hand discussion of this readily locatable on Google, but I haven't saved and can't readily find the posts from people actually involved in implementing Scala on .NET that I saw years ago that directly pointed to this as a problem.