1. You are assuming he is an elite back.
2. It's the only high level competition he really played this year unless you think Oregon's defense is high level competition.
3. Teams in the NFL will commit to stopping the run if he's the feature back. So, yes, he needs to be able to run against that and the defenses he will face in the NFL will be better than Penn State.
4. I don't get this blind love of Jeanty where nobody is allowed to even question how good he is because of the level of competition he played. Nobody has a problem with that when it comes to OL or DL that dominated lower level competition.