Yet on the spot guessing is what most product managers and executives require.

That hasn't been my experience at all (major bay area tech co). PMs and execs who I work with are generally totally okay with "I'll get back to you by [date] with scoping and ETA for that request." We even have a name for it: we call it an "ETA for an ETA". It's much better to give an ETA-for-an-ETA and then come back with a real ETA once you know the scope, rather than just guessing an ETA that turns out to be totally wrong. Sorry if that hasn't been your experience; being asked to pull ETAs out of your ass without doing due diligence sounds like it would be demoralizing.

I’ve also worked for major Bay area tech cos, and your description hasn’t matched my experience in any of them.