It wasn't that much of an exaggeration up until recently. De Gea's terrible distribution, combined with the players he was kicking to being poor at actually competing for and winning that ball, meant that we constantly just turned over possession after it went back to De Gea.
There's definitely been an improvement the last few weeks. On the one hand credit him for improving, on the other it's annoying that he didn't seem to consider his distribution a weakness he needed to improve on up until this time. Even if the manager didn't want us to play in a way to utilise that ability that much (which I'd believe with Mourinho, but not so much Ole), De Gea still should have been aiming to be better than he was.
You could say that about any player you choose, there's no point looking backwards now unless it can inform your knowledge of the player's future. End of the day they're not paid because they're rocket scientists, it's down to the club to buy/develop players and hire coaching staff that can work together to achieve their goals. When they don't, all the players end up looking bad.
Also, turning over possession when kicking long is not the same problem as turning it over when passing short. Clearing it in itself can be a good thing, though of course it's not always good enough. If the guys competing for the high ball and / or the guys who are supposed to be pressing don't do their job though, then that makes the keeper look bad, but not all long balls are a mistake.
Furthermore, if you look at De Gea's stats he's not actually been playing all that many long balls this year, I think he's roughly in the 30th percentile in the league? And more than 1 in 3 have found a United player, which isn't great, but not terrible, and either way gives you a chance to win the ball back high up the pitch.