If anything runtimes like the various JVM implementations, alongside the CLR and JS engines as well, are the bleeding edge of dynamic compiler optimizations with dynamic runtimes.

That is something that gets lost when talking about Java, yes the programming language looks like C++, however the JVM itself is heavily inspired by Smalltalk and Objective-C dynamic semantics.

Coming back to the spec, you will notice that it doesn't mention how threads are implemented, what kind of AOT/JIT are available, or what GC algorithms to implement, leaving enough room space for implementations.

One area where you are actually right, that I just remembered while typing this, are the way reflection or unsafe code hinders some optimizations, hence the ongoing steps that enabling JNI or FFM has to be explicit at startup, dynamic agents also have to be expliclity enabled, and the upcoming final means final (no more changing final fields via reflection).