I don't think people really understand character concepts in ARAM. There's a purpose in almost every character, and even characters that can be deemed "Useless" in the eyes of everyone else, can easily be used to win. Hell, I even won with Trydamere before, and he's considered one of the worst characters in ARAM. [ People need to try leveling his W instead... ]
I definitely do not agree with some of other people's choices of "Good" and "Bad" champions. It merely depends how you play them more than "this character is just worthless". Example, Fiora is deemed 'bad' in ARAM because people think she only has her ult in combination with the single lane and Ravenous. This is true, however, it's VERY easy to pull off her W's because people don't think too much, and just spam auto-attack when they get in range. Fiora can easily build some free damage by baiting auto-attacks this way.