I'm not aware how to get byte-for-byte identical source out of a Java class file or .NET assembly.

Last I checked, Java AoT compilation precluded runtime re-optimization, though I presume they've fixed that by now.

Last I checked, they both used stack-based bytecode, which typically takes longer to JIT and results in slower native code than a compressed SSA / control flow graph (see the SafeTSA papers).