If python 3 transition did bring dramatic perf increases I guess people would have been way faster to sell that upgrade to their hierarchies. Not that I blame python team for the lack of it. But fictional dev history would have been different

No doubt, huge perf improvements for free would have made the transition more compelling.

However, what I'm suggesting is that large perf wins are not free. Breaking compatibility too much more could have doomed Python 3. And now that the devs know how painful a transition is, they're far less likely to break compatibility again for any reason.