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.
You 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?
The 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.
