Whilst you have a point, it is more to do with the relationship between players than being useful in Ten Hag's system. It has been patently obviously for a number of years now that De Gea and Maguire cannot play together, there is no relationship between them and they expect different things of one another; that's not to say one of them is any more at fault for that than the other, they are just poorly matched in terms of what they instinctively do and want from the other.
In terms of being useful for Ten Hag's system, I completely disagree. I posted the below on 30th March in his performance thread so the figures may have moved around slightly but the general premise remains true:
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.
Essentially the general point being that it's impossible to play a high line with De Gea as while he's doing his best in terms of improving his game, he is still the fourth least likely goalkeeper in the league to deal with a ball in behind the defence & the second least likely in the league to deal with a cross into the box. You can't play a high line with a goalkeeper that wants to stay on his line, the two don't marry up and we'll always be making the game harder than it needs to be with him in goal.