Does not context play some sort of role in this debate?
De Gea, did not have the luxury of having Pallister and Bruce or Stam and then later a Vidic and Ferdinand ( during their optimum years) in front of him. Furthermore, during De Gea's peak seasons, United had a poor central midfield that was unable to control matches. Again there was no Ince, Keane, Butt, Scholes or peak Carrick.
If United were controlling matches, De Gea would not have had to make the saves he had to. The mark of a great goal keeper is to be there and alert when called upon. If United is a team challenging for honours during the 2014- 2022 seasons then De Gea is not heavily relied upon, which should be the case for a top team.
Thirdly, De Gea had a series of dinosaurs as his main coaches and therefore, was unable to develop his game to which "modern goal keepers" are now judged. Instead he was too busy making wonder saves and keeping United in matches they otherwise would have lost.
I feel if Ferguson had been around ( or De Gea had the benefit of a younger Sir Alex), he would have had the coaching to be a dominant keeper from opposing set pieces.
De Gea would have won a lot more if the transfer to Madrid had gone through, but to sum United up under Woodward and the Glazer's, they could not even get that right.