The other proposals I've heard for Java generics didn't monomorphize at compile time but instead modified the .class format to represent generic classes/methods

The other proposals I've heard for Java generics didn't monomorphize at compile time but instead modified the .class format to represent generic classes/methods closer to their source representation. Because the embedded systems at the time that cared about code size in Java would have been structured as bytecode interpreters, they arguably would have had smaller binaries without type erasure. The casts the erasure does under the hood are represented as additional bytecode at most call sites, but would have been implicit if generic functions had first class JVM support.