Going to https://lolalytics.com/aram/worldwide/platinum/plus/champions/ and clicking on every champion and comparing their overall win rate to their win rate with Triumph, gives a higher win rate to 134 of 140 champions.
Exceptions
Lower win rate with Triumph than overall: Rakan, Shaco, Zilean
Too low pickrate to show up on lolalytics: Janna, Nami, Soraka
So fun and balanced.
Quiet Dude4 votesYou have a wealth of things to nitpick, and you choose the one where everyone takes a mastery that gives 12% of their max health per kill/assist in a literal "just for fun" game mode where they can't recall back to base to restore health?
my waifu Taliyah1 votesThat's the point. They can't restore health, but they can anyways because Triumph.
Quiet Dude2 votesTriumph is balanced in summoner's rift. Runes and masteries usually aren't balanced for anything else. If you don't like it, try picking up an item that lets you apply grievous wounds.
Killer of Night91 votesThe only thing unhealty in aram is dark harvest on ranged champ (getting oneshot by an adc with only IF+dark harvest isn't funny). Even comet who suppose to be the strongest because it's a poke rune is good in this mode. Btw triumph is good as it is and i think it's well balanced. Maybe grasp/predator should be more useful in this mode.