I don't think he's better than them to the tune of £80m, though. And thinking about it, I'm not sure he's that much of an upgrade on what you already have. He's a good centre-back for a team outside the top six, whose ambitions are probably 7th and a good cup run, but as the leading defender of a team whose ambitions are to compete in at least three competitions and make the top four? I guess there's only one way to find out.
I'm not sure why but this summer feels like a moment for United. As a couple of other posters here have mentioned, you're just not the team you were when it comes to drawing in the genuinely top talent, which is why Maguire is your "best option". De Ligt was never going to come in, your big money signings from three years go already want out, and for all the money you've spent already this summer (£130m~ if you include Maguire), you're not really much closer to finishing 4th than you were last season.
Interesting times at Old Trafford.