I thought about this after watching a game with Jax, Lee Sin and Kata who could do it and suffered for Pantheon's limits. I'm not complaining, I'd just like a reasonable explanation u_u
vs. 
Lumus Avatar4 votes"Ah, there's my ally, safely out of combat - where I'd like to be! I'll just nimbly jump in the air and SMASH THEM IN THE FACE WITH MY SHIELD. Thanks for helping a brother out. Make sure you run when that stun wears off, it looks like the fight is moving this way."
Pantheon scampers into a bush from which he man-leaps all the way to dragon, killing the enemy jungler and grabbing the buff for his team. The laner he jumped to was never heard from again
Raw3 votes[deleted]
Long Dong Wukong3 votesJax and Katarina's do damage, the stun shouldn't matter. They just make it not stun just like Jax and Kat don't damage allies.
But the reason he can't ally jump is because he has an Ult that places him where he needs to be. He doesn't have additional mobility because he has the ability to plop right where the fight is, and he's not supposed to run away once he's there. He's basically a "surprise mother fucker" champion.
SmokingPuffin2 votesPantheon is an all in champion. He can't dash to allies for the same reason Braum can't dash to enemies.
Darth Valer2 votes Leap Strike: Jax leaps to target unit, dealing physical damage* if the target is an enemy.*
Shunpo: Katarina teleports to target unit and gains 15% damage reduction for 1.5 seconds. If the target is an enemy, the target takes magic damage.
Well, he works a little bit differently, but you got my point u.u
Aegis of Zheonia: Pantheon leaps upon a target enemy unit within 600 range, dealing magic damage and stunning them for 1 second, while refreshing Aegis Protection if the target is an enemy (this time I added it u_u).
Most assassins haver reliable escapes, if he had one like this he would be top tier (if he is not already xD) imho.
Jefftiffy1 voteshis shield stun is sets up his entire burst and isn't really a distance closer so jumping a whole 600 units just to stand there like an idiot doesn't make any sense. Plus you are hitting them with the shield that is even in the animation, so why would you hit your team mate to run? Jax merely jumps to them. Katarina blinks. Lee Sin dashes to the target and doesn't even touch them. Pantheon smacks them with his shield.