Every one of England's rivals will be surprised and pleased that Grealish isn't in the squad. He is well known throughout Europe, at club and international level. As an English player, he's a bit alien, he stands out. Teams worry about him because he holds onto the ball and keeps you on the back foot. We know this first hand from coming up against him. As a fan, you're not comfortable when he's got the ball on the left because you know you've got your hands full to get the ball back, and he's unpredictable - you just know you're going to have some defending to do because he'll rarely lose the ball until he's in the penalty area / a decisive area.
I'd actually say his omission points to a fundamental lack of understanding of football, particularly in the attacking area, from the manager. It's quite incredible.
At least 2 of those attacking selections will be a complete waste of space.
Maguire's absence is the icing on the cake.
This should have been England's tournament, but we've found a way to waste yet another golden opportunity. The defence will be a liability, and the youthful, lightweight attack will hit a brick wall when it matters, despite all the quality - if recent friendlies are anything to go by.