In Aram there is a global debuff where the healing and shields you recieve from other are 50% weaker. Meaning you need 2 heals in Aram in order to recieve the same amount in SR. Also there is
,
,
,
,
and
that apply Grevious wounds that makes 40 % incoming healing weaker.
For example if the ability states it heals 100 HP in SR then every time you cast it in Aram you get 50 HP, if you apply grevius wounds then the 40% of 50 hp is 20 HP. So in total the players can recieve way less healing and when there is problem with damage creep and a broken rune in Aram called dark harvest( the new one is still as busted as the old one i can confirm it) which is very easy for ranged champions to proc it like caitlyn,karthus,jinx,varus as well some other champions like wukong and kayne it becomes less problematic. I mean for the same healing in SR they have to cast twice and waste twice the mana.
If they reach late game with full build with mana regen, Warmongs, redemption etc then sorry to inform you but late game kassadin or mundo or volibear or garen or darius or ornn or xerath can oneshot you the same even with all the heals from sona/soraka/nami. I am talking from personal experience as i have 2.5 k games in Aram and playing almost exclusively aram games right now in the preseason .