There's the saying of to build a title winning side you build from the back and the gk is the very first point of the back and is why we won't be top side with de gea as that first point, look at the turn around when pep and klopp made changes to their gk position.
Fans are really over estimating how hard it is to replace de gea, there are plenty of shot stoppers out there as good as de gea and that is all he excels at, just look at how easy chelsea found it to get a competent goalkeeper without breaking the bank.
I would still prefer Henderson over de gea as he still puts us on a path of a more progressive style tactically and as seen with England and City under pep, despite the errors that lead to goals from first implementing playing out from the back, they had to endure those teething problems to reap the rewards in the long term
Think that's going too far the other way.
De Gea is one of the best pure shot-stoppers in Europe. There's no point in downplaying how good the one positive aspect of his game is. The issue is whether he's one of the best all-round goalkeepers and he isn't.
But even then, as we saw in our struggles to replace Schmeichel, there's more to being a United goalkeeper than just what you offer on paper. I could point to someone like Robert Sanchez as being a better all-round keeper on paper but that's without knowing his personality and how he will handle the step up from Brighton to United. And whatever else we might say about De Gea, he showed uncommon mental strength to stick through two different spells of the sort of heavy criticism that would (and has) seen other goalkeepers buckle at United, which is a quality neither stats nor just watching games would tell you. You also need proper scouting into what they're like off the pitch and how they're likely to cope under that pressure spotlight, as we had when we signed De Gea.
There are better goalkeepers than him out there but picking the right one isn't
that easy. We don't want to go through another period of changing goalkeepers every few seasons.
I mean you mention how easy Chelsea found it to find a goalkeeper, but that came after they wasted a record transfer fee on Kepa who is much worse than De Gea. With everything else we need to do, wasting £60m+ or whatever on someone who doesn't make it would be quite a big problem.