de Gea has both a huge reputation and stats backing him up. if you look at xG f.e. (https://understat.com/), United conceded 15.54 goals less then they should've in 2017/18, that's better than both Oblak and Alisson.
Besides, it's not like Oblak is given a poor rating in FIFA 19, he's on 90, that's hardly criminally underrated
Yes 90 is a quite high rating for a criminally underrated gk!
De Gea is by far the best gk in the world at the current time, he’s the main man for MU. I watched a couple of their games last season and the guy can come up with some nasty saves, all game long. It’s crazy. MU are lucky to still have him.