No, we know how to optimise all these issues. They're solved, through a combination of online profiling, inline caching, splitting, deoptimisation, scalar replacement, etc. (I wrote a PhD on it.) I don't think you could name a single Python language feature that we don't know how to optimise efficiently. (I'd be interested if you could.) But implementing them all is a difficult engineering challenge, even for Google, mainly because it involves storing a lot of state in a system that isn't designed to have state attached everywhere.
Yes, that’s what my reply means, your “no…” is poor communication style. If you think you can do better than the folks working on it for a decade plus, by all means step up.
I'll give you one you could have used - the GIL - however I'm not sure the GIL's semantics are really specified for Python, they're an implementation detail people accidentally have relied on.