I think JT is playing fine. It's just that no one around his is playing very well. This has been re-hashed ad infinitum, but that's to be expected with:
Laskey (co-starting BB): NFL roster
Days (co-starting BB): NFL training camp
Smelter (starting WR): NFL roster
Waller (starting WR): NFL roster
Mason (starting OG): NFL roster
That's serious talent that moved on to the highest arena of football. And it's been replaced by a bunch of freshman and sophomores.
I can't explain the offensive line struggles, but JT without 4-5 NFL players around him is clearly not able to do as much. I'm not sure that he's any more beat up - he's just not able to distribute to the graduated guys that are (at least for now) much more talented.
I love the potential of Marcus Marshall, MLD, and Jeune. But right now they're not close to Laskey/Sims, Perkins/Zenon/et al, and Smelter/Waller. They'll improve as the season goes along, but it's never truly plug-and-play.