I've been corrected in how the deal went down, but it seems to look worse and worse. The Patriots contacted the Colts and either asked for Dorsett or asked for what the Colts would give for Brissett, as they were trying to trade him, and they accepted the offer. That seems pretty idiotic, or at the least, it seems like a terrible approach to maximize the value on a trade, but it seems to be the same way the Garappolo deal went down as well. There were GMs commenting to writers about the Garoppolo trade that they had no idea he was available, but the 49ers got a sweetheart deal as the only bidders. Call one team and take their first low-ball offer rather than actually getting value for better players/draft picks, in the midst of being very short-stacked when it comes to young talent.
Even if Dorsett ends up being good, this was still a bad deal, and it's crazy to think that there's no market at all times for a good starting or backup QB when teams are still trading multiple high picks to move up in the draft for college QBs but rarely any other position. I think the Patriots themselves were trying to move up themselves this season to grab a quarterback (not sure which one, or maybe more than one.) Yet they just gave away a couple of QBs that are valuable to other teams and got a whole second round draft pick to show for it.
You seem to be assuming that BB just called the Colts randomly and out of the blue, without him, Caserio, Adams and others having done their homework on the state of the Colts roster - and everyone else's.
I mean, these guys aren't exactly the NSA, but they certainly maintain a file (+tape) on pretty much every player in the NFL - files that, in many cases, were probably started back when those players were juniors, or even sophomores in college. They certainly have records of all their prior dealings with players' agents. They probably have a file on nearly every NFL coach from the positional level on up - their scheme preferences, their playcalling tendencies, their training methods, etc. They also know the GMs and personnel guys from all the other teams - how to approach them, what kinds of deals might appeal to them, how much they're likely willing to pay, or to ask for, etc.
They've done (and proposed) a lot of deals themselves, over the years, and probably have more accurate information on a lot of deals that didn't involve the Pats than we'll ever know.
In short, these guys know a metric crap-tonne of stuff that WE have no idea that they even know - because it's their damn job.
It seems to me absurd to think that Caserio and his staff don't have constantly-updated, player-replacement contingency plans in place for pretty much every situation. It's not really significantly different than maintaining a draft board. It seems absurd to me that anyone thinks that BB goes into any deal blindly.
When the Pats suddenly lost both Edelman and MM late in Camp, Caserio probably had a half dozen potential replacement WR acquisition plans to present within a couple days. There was some sort of discussion among decision makers that ranked those deals according to lowest "cost" (in terms of players, 2018 draft picks, cap hits, etc.), and ranked according to the likelihood that each deal could happen quickly and without much extraneous bargaining. Apparently, BB's call to the Colts was at the top of their list - and the deal got done. If it hadn't, there was another deal ready to be tried with another team for a different WR (that may or may not have involved Brissett).
And, no, I'm NOT making this up.
This kind of thing is NOT unique to the Pats. Most good FOs do something very similar. Last winter, I read a fairly long article describing in detail how the Seahawks' FO handles acquiring injury replacements. The readiness and the process for them is pretty much what I've describe above.
Sure, every team gets calls out-of-the-blue, like the one Lynch made to BB about JG. But it's not as if BB was at all unprepared. Sure, sometimes the players that the Pats acquire end up not meeting the Pats expectations (or ours). None of that means that BB, Caserio, et al, didn't perform due diligence and follow their best estimates.
The fact that we don't know or understand all the sh it that these guys work through for 100 hours a week for most of the calendar year does NOT mean that they're freakin' bumbling idiots who are simply making sh it up as they go along and, thus, getting constantly screwed on deals when OBVIOUSLY there were MUCH BETTER DEAL out there.