I think that somewhere Riot said that if a champion felt bad to play against or unfair then they would be eligible for a rework.
Pantheon seems like the perfect target for a rework.
I feel like if he got reworked him being a gladiator should be explored more, so that his auto attacks are more important than to proc duskblade. It would make him more of a duelist and not an assassin. Also, he still has the Targon aspect of him, but he isn't a possessed person. He's the warrior for Targon.
My proposed rework kit (take this with a grain of salt since I'm not on the balance team and don't know what would be healthy for the game):
Passive:Whenever you take damage from an enemy champion, you deal (1-3-5-7-9)% increased damage to that one champion, but deal (5-4-3-2-1)% decreased damage to any other champions you damage in that duration. (Scales off levels 1-4-9-14-18) (Lasts for 10 seconds before not being able to be procced for another 10 seconds)
Q: Passive: Your auto attacks and abilities deal (10-20-30-40-50) adaptive increased damage towards "Vulnerable (like Brittle but you do more damage)" champions.
Active: Increases attack speed by (10-15-20-25-30)%. Also, every 3rd auto attack makes an enemy champion "Vulnerable." Lasts for 8 seconds.
W: (its a skillshot) dash forward, dealing damage to anything in your path. If you hit an enemy champion, it makes them "Vulnerable" and it deals (10-20-30-40-50) attack damage. (range of a slightly longer Quinn E)
E: Melee Range: You stab your spear through the enemy's foot, rooting them for (1-1.2-1.4-1.6-1.8) seconds, and dealing (30-50-70-90-110) attack damage. If they are "Vulnerable," it roots them for (2-2.2-2.4-2.6-2.8) seconds, dealing (60-100-140-180-220) adaptive damage.
Ranged Range: You throw your spear, knocking the enemy back, dealing (10-20-30-40-50) attack damage, rooting them for (.5-.6-.7-.8-.9) seconds. If they are "Vulnerable," it deals (20-40-60-80-100) adaptive damage and roots them for (1-1.2-1.4-1.6-1.8) seconds. (Range of Pantheon's current Q)
R: (only usable on "Vulnerable" people) Summon the power of Targon to launch you into the sky to land on a single enemy, knocking them up, and dealing "50-100-150" adaptive damage. (cooldown: 35-25-15 seconds). (range of a level 1 Ryze ult, range never is increased).
I feel like this would make a more splitpush oriented Pantheon and not an unwinnable lane bully Pantheon. As I said at the beginning, take this with a grain of salt, since I'm not on Riot's rework team and I wouldn't know whats good for the game.