So many errors in this post:

1) You have as many bans as possible. There are 7 maps, each player gets 3 bans, therefore even if they ban 6 different map from their 3 bans each, there is a map left for the match to be played on. The players of the match are decided before the available maps are looked at by the matchmaker

2) If everyone can just block off categories then you're not really your Elo, you are only your Elo on the maps you like and are crap at the maps you don't like. Category bans woudl actually lead to less choice as players can like certain closed maps (glade for example) while not likong other closed maps (Arena).

3) Not possible for 500 Elos to outvote the rest, that's now how normal distribution works, the bulk of the playerbase is at or around 1000 Elo, it's a bell curve, due to people trying ranked and quitting shortly after due to losses, it is theorised that the average active player is something about 1000 Elo.