That would not be QoL buffs, that would be changing his dynamic entirely. He's meant to fall off as his early-game is really reliable, along with being able to teleport a bunch of the map whenever necessary.
Also, consider handing some killing blows over to your allies when you're jungling and are certain your team has the time to give the killing blow to a specific person. If you'll fall off like you said, wouldn't it be logical to give them to people who won't?
Are you buying a Last Whisper, too? Pantheon is noticeably less powerful later in the game and strongly countered by armour, but his low cooldowns give him a bit more potential than most other AD casters later in the game, and he'll be pretty good clean-up for a good initiation if you have Last Whisper to alleviate the issues of your main counter.