I'm guessing you haven't played the very first URF?
When everyone got to pick what they wanted to play and had an equal chance at winning the game. Now, games are won in the champion select. It completely depends on which team got the better RNG on champ picks. That's usually how ARAM is won.
Have you ever been forced to go mid as say Ivern and you were vs a Katarina or Zed or Fizz in URF? It's not fun and I guarantee if you had the choice you wouldn't have gone Ivern in the first place.
Their reasoning was to keep the game from mode from developing a meta and being stale, that's just a way of getting around saying we're trying to balance URF. All they had to do was add 10 bans like everyone was asking for (at least they're starting to be less stupid and give more bans in actual games I guess) and the mode was 100% perfect. Everyone gets a ban, the "meta" champs are dumpstered and we all live happily ever after.
Also the not balancing game modes was a lie, they disabled karthus and teemo in (I think it was one for all) because of balance issues. A lot of the hate comes from Riot blatantly lying and ignoring the community. Nobody is gonna support that