Wild speculation: Could the extra speedup be due to some kind of JIT hotpath optimisation that the previous reflective non-inlinable call prevented, and which the new use of the single `arrayLength` bytecode enabled? E.g. in production maybe you're seeing the hotpath hit a JIT threshold for more aggressive inlinng of the parent function, or loop unrolling, or similar, which might not be triggered in your test environment (and which is impossible when inlining is prevented)?