I've read that it can take a long time to get over ACLs

It's one thing to be medically cleared and able to play; it's another before the injury is fully healed and back to normal. At least this is what I've read.
So indeed Wentz may not be himself this year.
And, it may be that because of that injury, he now has a mentality that isn't so cavalier about his body. And since running around has been such a part of his game, it may be affecting his overall performance.