just remember, you actually need to build armor (cloth x5 health pots, armor seals, 1 point in armor mastery), and he falls off massively, just like his late game. If building defense, it wont matter if he tanks a turret shot, cuz you won't take much if any damage cuz his damage will be falling off. And its not op. Thing is, turret diving one of his only real times to get a kill. Nobody, in the early game, would trade Panth 1 v 1. Because of this, one of the only real times to kill the enemy is under a turret. Man Dropping on an enemy while B'ing under turret, is what makes pantheon, MANTHEON. Also, getting kills doesn't really help him once the clock ticks 35:00 min in.
Trust me, ~2000 games played as panth. Remember theres two points to the game, (winning the lane, which seems to be the world to everyone) and winning the game (which are two different stories for Panth). Panth may win lane, but its harder for him to dominate the game.