Variation of Merc Tread's Passive in Howling Abyss Aura

Part of the howling abyss aura should have to do with chain CC. Enemy team has Cho gath, Blitz, Naut, and Vel Koz you have nonstop silences, knock ups and stuns and slows. Not to mention two of those champions deal high amounts of true damage. I don't always have time to play League so I usually do a quick ARAM to try to get the first win IP, but on "random" comps with chain cc like that and no relief from it aside from Mercs or QSS, it makes ARAM terrible to play.

Also, WHY do champions get true damage???