So is Martial a "top four" striker then? His goalscoring record over the past few years would suggest not, and he's our player rather than an emergency loanee (who btw has started every single game since we signed him).
The question was would those clubs would swap their goalkeeper for De Gea, not if you would. And I don't think they would, certainly fans of the three clubs I mentioned wouldn't, but then they probably recognise the benefits of a goalkeeper with the capability of leaving their line occasionally and passing the ball to a player when under pressure rather than a supporter. You're substantially underrating Jose Sa btw, he can be erratic at times but he's a much better goalkeeper than Martinez for example. Pickford I'm no great fan of admittedly but there's zero chance a team managed by Sean Dyche are taking De Gea over Pickford purely for the higher line Pickford enables; which is the same story with Pope at Newcastle, Meslier at Leeds & Kepa at Chelsea. Brighton and Brentford wouldn't touch him because, well, they focus completely on data analytics in recruitment and De Gea flags up horrendously on pretty much any data driven model, plus realistically they ask a lot of their goalkeepers in possession and Raya and Sanchez are streets ahead in terms of pure distribution.
Talking of the defensive line, given that we've now got what should be a considered a reasonable defence for defending high up the pitch; our defensive average line height is the 3rd deepest in the entire division; with only Forest & Bournemouth deeper on average, and literally less than half a yard deeper at that. We've got a goalkeeper that, although vastly improved at sweeping behind his defenders this season, is still the fourth least likely goalkeeper in the league to intercept a ball in behind the defence. There is a clear link there whether people like De Gea or not. And then when you look at how Ten Hag wants us to play, which thus far has us playing more of a possession game than recent seasons when everyone is available, which is backed up by only City, Arsenal Liverpool, Brighton & Chelsea having higher average possession stats than us, the difference is that their average defensive lines are the 1st, 2nd, 3rd, 4th & 7th highest in the league (with Newcastle being just behind us in the possession averages & 5th highest line). For completeness, the outlier in that is Brentford who have the 6th highest average line but lower midtable level average possession, but they have a goalkeeper who both sweeps high and progresses the ball exceptionally well. Possession and high lines go hand in hand, as teams that maintain possession will generally compress the play into higher areas of the pitch and look to play around teams in tighter spaces; we are hamstringing ourselves if we continue to play a such deep line and attempting to be a high possession team as we won't be able to compress the play, there will always be more space between players and passes will therefore be riskier (not to mention the space makes it more difficult to win the ball back quickly). I just don't see how that changes without the goalkeeper changing.