Actually Mead didn’t pick the ground at Gettysburg, it was Gen Buford who got the high ground.
But it was Mead who chose to stay there and fight, rather than fall back to the Pipe Creek position he had previously chosen.
Meade arrived and could have ordered the army to fall back, but he didn’t. He chose to stand and fight there. Reportedly, he relied upon the Council of War of his general officers in making the decision, but still, the point remains that he could have decided differently. Of course, Meade’s decision making during and after the Battle of Gettysburg was questioned a lot both during and after the Civil War. He was an overly cautious commander, perhaps, but at the time of Gettysburg he had just been appointed to the top command and had not had time to become thoroughly familiar with his forces. I’d say he did pretty well for the situation he was thrust into suddenly..... it could have turned out much worse for the Union.