And then we find out that Smalltalk implementations might choose to optimize instead of allowing anything to change at any time.

    ifFalse: alternativeBlock 
        "Answer the value of alternativeBlock. Execution does not actually
        reach here because the expression is compiled in-line."

        ^alternativeBlock value

Strongtalk limited dynamic features.

But you’re not wrong in general. Even for Python there’s PyPy, with a JIT ~3x faster than CPython.

There's a pretty big gap between "its JIT research eventually became Hotspot" and "Smalltalk can be made to perform on a par with Hotspot."

I was pointing examples of the opposite, that JavaScript is less dynamic than Python.

There's lots of Python code out there that relies on not using slots. If you're making a JIT, you can't assume that all code is using slots.