Far from it, Go was designed to be optimizable form the start. The GC was obviously not optimal, but the language semantics were such that the GC can be replaced with a better one with relatively minimal disruption.
Of course one can't release optimal code from version one, that would be absurd.
Also your last sentence is extremely condescending.
Go’s GC was intentionally slow at first. They wanted to get it right THEN make it fast.
No offense but you’re not making a strong case. You’re sounding like an inexperienced coder that hasn’t yet learned that premature optimization is bad.