It's not about being "happy" that he is gone or even that we didn't like him personally. The reality is that Grant's performance on the field was mediocre at best. This year, his NCAA QBR was 54.5. That ranks him 82nd out of 125 ranked quarterbacks. He had 16 touchdowns against 13 interceptions. Compare that against one of the top quarterbacks, Kenny Pickett, who had 42 touchdowns and 7 interceptions with a QBR of 81.2. If I recall correctly, Grant's QBR ranked him around 60th last year.
As far as I know he is a good kid and I wish him the best but his performance on the field, which is what matters in football, was not at the level we need if we want to win championships.