joy of even when you think you're picking a franchise QB, you more often than not are not picking one who changes everything for you and can hard carry a roster full of holes until after you can pay him (like what has happened in Cinci).
This is the exact mechanism of the Bears rebuild (1st overall where Panthers selected Young). Now you still have to draft well at those spots you move to, but unless you absolutely LOVE that QB and think he's the one to turn around your whole franchise, your margin, imo, is much better getting a whole haul of picks and players rather than a lottery ticket given 1st round QBs have a less than 50/50 shot of even being a "franchise" QB with GMs being notoriously bad at knowing who's good and who's a bust.
I get that everyone thinks they "need" a gamechanger QB, but your margin for winning goes up exponentially if you actually build a roster around a young dude rather than just keep swinging year after year after year, especially given your QB gets thrown to a shit storm without a roster around him (hence why Williams looked like ass last year, people thought Young should be out of the league, Darnold is doing well with a place that didn't draft him, and now on a competent roster, they're doing just fine even if they're not Mahomes or Allen). Instead we've got 4 teams left that built elsewhere then plugged in their QB once they found on they loved either in the draft or via trade. I get what you're saying and if there was a guarantee, sure (hence the why you only do it if you love the prospect, because someone always does and will trade you a bunch of assets for them). No reason not to abuse people who will overtrade assets to jump start your rebuild when you're so far away from having a full roster that can compete like the Raiders are.