I'm not convinced Jose deserves as much blame as the board for this transfer window. Whichever way you look at it the latter are failing in their role; if you no longer have faith in Jose you sack him and get someone else, you bring a DOF in to manage transfers, if you back Jose in the manager's role without a DOF you back him in the market. If they had longstanding doubts about Jose and didn't act they're spineless, if they just started having doubts after a shell of a preseason tour with barely any senior players they're stupid and if they back Jose to manage the team, have money to spend, but vetoed his shortlist then that isn't backing him at all in the current structure minus a DOF.
If you think it's likely Jose has mishandled players, such as Pogba and Martial, fair play to you as a fan for formulating that opinion over the last few months, and solidifying it this summer, based on the information available. The board have no such luxury. They should be well across this issue, which has been a talking point in the press at least since January, and have a solid plan that enables them to act prudently for the good of the club. If the perceived rift between Jose and Martial and Pogba is a deal breaker regarding trust between board and manager they should have got to the bottom of it towards the end of last season once and for all and acted over summer to back Jose or bin Jose. What we have now is a ridiculous halfway house where Jose is in place but clearly not backed, and it's the squad and ultimately the fans who suffer.
To be fair your second paragraph covers the board's potential culpability well, but I would go further in saying the buck stops with them now, not in a few months when it may be all too clear how badly they've managed this period.