he is simply an extremely weak champion, thats why nobody uses him. he has decent earlygame power but not more than other strong earlygame champions (less than elise, rexai, lee sin) and he doesnt scale AT ALL. like he literally has NO SCALING POWER. either you end game by 10 minutes or there is no reason to pick pantheon.
like if you look at it, pantheon is not a bruiser nor is he a real fighter, he is really a low range mage who scales on AD. his main damage is his E which is a channeled ability so it can be interrupted and its pretty low range. also he is full squishy so he cant really "catch" anone with his W and even tho his ultimate is good for 10 minutes into the game, its not a combat ultimate so in fights he simply has no ultimate which is a big loss.
then again even tho his Q is good for jungling and decent for laning, for fighting it is actually very weak especially since it scales so badly with levels that leveling it up is almost not worth it at all and its range is so low that you cant poke most champions with it without dying.
another problem is that he scales only on AD, armorpenetration and cooldown reduction and there is only one item in the game which gives one or two of these stats without any other useless crap you pay for without needing it and that is last whisper.
basically there are no items for pantheon to scale with. the jungle enchant warrior is pretty good but after that, what you gonna buy. probably another brutalizer but you cant really build it into anything. black cleaver is okay-ish but the extra hp is unneccessary and the armor shred stacks up with your E so you actually somewhat need a second E to fully utilize its damage, which mostly you dont get and also dont want to get, especially on squishier targets.
essence reaver is decent but the life and manasteal are not really neccessary but cost alot of gold. the best "build" on pantheon is probably jungle item -> bf sword -> bf sword -> bf sword and ionian boots and basically end the game.
