It's not just about being a sweeper keeper. It's about almost everything that isn't just making saves from longer range efforts. That's the problem. De Gea has massive holes in many parts of his game. That's why people like me complain about him. Him and a lot of our fans think that making a few saves is enough for an elite level goalkeeper. It isn't.
Our defence has almost never looked good in the 10 years he's been here. He is the only constant.
It isn't the only constant.
We had Henderson in goal, yet looked ever worse.
We had Romero in goal and kept clean sheets against poor teams yet poor against the rest. Realistically no difference Vs DDG.
We had Valdes in goal and looked awful,
Now you could argue that these be keepers are not the best, and you'd be right, compared to DDG they can't hold a torch.
But Henderson was meant to be a playmaker with his feet, yet still not as good as DDG,
So no, DDG isn't the only constant.
The only constant is United not improving the midfield duo/holding midfielder to improve our defense and stats such as shots faced etc etc etc.