I think that the communication problem here lies in nuance.
It's overly reductive, IMO, to label either signing "good" or "bad". In retrospect, I bet United wishes they'd gotten the Madrid deal done, had replaced him with a comparable keeper on lower wages, and had reinvested the proceeds and wages in the squad. (Assuming Woodward hadn't screwed it up, which he might well have.) That said, de Gea was spectacular for years before that. They don't regret bringing him in initially, for sure. In his heyday, he was probably worth a good ten points a season or more.
The Alisson deal absolutely made sense in the immediate term, but it remains to be seen if they mortgaged the future to get those titles.
There are signings that it's easy to say were "good" (DCL) and ones that were obviously "bad" (Delph) where extreme value for the money was, or was not, received. Not all signings fit neatly into those categories. I would argue that the de Gea situation is more complex and that the Alisson deal may (or may not) turn out to be.