I've yet to see a single Zed, Nidalee, LB, Katarina, Qiyana, etc. NOT be a huge threat even when the player behind it definitely had no clue how to play it. And when a main picks it up, the game is over before it loads in.

On the other hand I've seen plenty of one tricks or dedicated mains having their nerfed champion given to them and being unable to do basically anything, if they go damage they don't deal any, if they go tank they are oneshot by half the champions.

%dmg/dmgtaken changes for the sake of trying to achieve close to 50% winrate IN A HEAVILY RANDOMIZED GAMEMODE is absolutely idiotic, and whoever came up with it should really think hard about how he got into a position at Riot where he was able to make this decision.

And "oh but hard to play champions will be useless when given to a player who doesn't know how to play it". To that I can say:

ARAM gives up to two rerolls per person. Use it.

I've yet to play an ARAM game with less than 3 rerolls used across the team. In most ones everyone rolls once. And if the player cannot play ANY of the possible champions AT ALL, then it is his lucky day to learn so (or dodge). But not by making that champion unkillable and one-shot everything by farting in their general direction.