After the ARAM changes losing early inhib is really punishing which puts poke champs & ADCS at the top of the winrates. Sona, Ziggs, Maokai are the storngest champions in ARAM with Sona having a 69.7% winrate, Ziggs having a 67% winrate, and Maokai have a 66.5% winrate.
Before the changes to ARAM were super minions buffed your minions you had gold gen items in ARAM coin, spell thief, relic. Relic made melees playable since they were punished less by poke. Though spell thiefs did make poke mages have higher income tanks were actually viable in the early game without being severely punished.
ARAM also has a history of being plagued by ARAM only accounts where they only own the top tier aram champions. I'd like to see a system put in place where owning x amount of champions will let you choose between a few champions say 80 champions for a choice between 2 and every 20 past that will give you another choice. If a system like this isn't put in place maybe owning most of the champions should grant you 1 reroll and owning them all should grant you 2. Currently you cannot gain 1 reroll per game as you need 250 points for a reroll. The current formula is 30 points + (1 x # of champs owned) meaning you will only get 167 points per game if you own every champion.
It's almost impossible to balance ARAM purely because of the fact the every update SR has it will go to ARAM.