Eh I think that's true and not true...
NFL teams draft on upside all the time, even if that upside won't hit very often. That's a huge % of the value of any draft pick and any new head coaching hire as well. Hard to see the BB upside for some of these young mediocre teams. Makes a lot more sense for a very good team that just needs to avoid having a below average coach, but that opportunity hasn't presented itself (yet).
Like the bolded is true, but it's true because everyone you're drafting has zero track record in the NFL - and even picks that are supposed to have a 'high floor' still flame out a lot more often than former all-Pro players do.
Certainly this doesn't happen often (maybe only 10-20% of the time?), but when it does, it's massive. Hires like McVay, Shanahan, Harbaugh etc. are hugely valuable. Just because it's not that common doesn't mean it's not a big factor in the hiring process. A lot of teams are willing to risk hiring a potential flame out that's likely worse than BB will be over the next 2-3 years for the chance at a long term solution.
Basically, a short term dud of a hire is not as bad as a long term homerun hire is good. BB is going to have a higher likelihood of being at least OK for a few years (and maybe that's all a team like Buf or Dal needs), but most of bad teams without a coach are hoping for more.
I agree this is what's actually happening, and even that for some teams that are looking at a decade-long rebuild it could be the right call... but I think the risk/reward is a lot closer than you're suggesting. Buf or Dal needs 'ok' like tomorrow; there's a number of teams for which 'above-average competence' could mean playoff contention within 3-4 years
But bigger-picture, I think your point also hits on the negative aspect of this - which is that Owners and GMs also want to have that massive 'home run hire'. The funny thing about this coming full circle is that I'd argue R Kraft is a prime example of this, where (even in other threads here) his decision to hire BB is a huge part of what gives him 'what a smart owner' credibility, and every other owner wants that
I dunno; I feel like you see this a lot across sports (hell, I'd argue it's at least part of what people dislike about Bloom, fairly or not), where some GM/owners want to
win (as in the championship), and some want to
"win" (as in seem smarter than the other GMs & owners) - and the former has more success, because the latter wind up so focused on whether they're able to find diamonds in the rough or win every trade or avoid embarrassing failed FA signings that they never actually push the chips in to trying to win a title.