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.