My biggest problems are increased dodge rates and no longer getting to play certain champions.
In aram, there are champions that are really good, and then there are those that are just terrible. The ban feature has just made it so people don't roll those good champions anymore which is causing people to dodge the queue way more often than before. Where is the fun when all the good champions are banned and all you are left with are the crappy ones.
When we played aram back in the day in the custom game mode the goal was to get stuck with a randomly generated team and try and learn the champion you get stuck with and make the team work. The only time people would dodge back then was if they got stuck with a terrible champion and they wanted a chance to get something that is at least slightly better, it kind of ruins the purpose of the gameplay but there wasn't a lot you could do about it. Adding the reroll feature helped the dodging problem and also made balancing your team a little bit easier. It's still pretty close to the same game as we made back then, just with enforced rules.
With this ban feature, you are changing the original gameplay rules by modifying the champion pool so you never get to play those good champions anymore. It is throwing off the balance. With only a few good champions to pick from now, if one team rolls them then that team has the advantage and the odds of rolling a second good champion is so low that it most likely won't happen. Previously there were enough good champions that even if one team rolled them there were enough for both teams to roll great champions, and sometimes you would still have to reroll those good champions for a better chance at a balanced team.
I no longer get to play teemo, lux, veigar, and ziggs for the most part since they are practically always banned. Then there are also the 6 other champions that get banned which usually are ones like Xarath, Varus, Jayce, Brand, Pyke, Illoai, Zilean, fiddlesticks and maybe 1 or 2 might be the less popular ones.
aram is ALL RANDOM all middle, (middle is no longer applicable since we aren't playing in summoners rift anymore), It's supposed to be 1 random champion picked from all of your available champions.