so, im in the same elo range as you. and im particularly good at mid and support. so, when i go into a ranked game, while i can fill any of the required roles, i feel as though i can carry better from my two aforementioned spots. as such, i'll enter and say "mid or support plx" but i think people should have one or two main roles, in which they have a variety of champs they play well, and then at least two champs or every role they dont main. when i get put top, i go tanky dps nidalee or nautalis, for example. so, i guess people dont have to be equally carry mode at every role, but rather have some champs that they can fill each role with, then have their main roles. in all reality, at a higher level, or if you have a team, you'll end up maining a role or two, which is simply the roles your going to be better at, just because you play them more. also, ask yourself this; if im at 1400 elo, and i main top, and i go against someone who merely filled the role because they had to, do i not have a higher chance of winning, and, by extension, would you not prefer to have the guy who called top go top, then the jack of all trades top?
also to those kids that say support is easy role, your stupid. some supports are easy to play, as are some mids, some jungles, some tops........ janna is a hard support to play by any means. she has skill shots, a shield that requires reflexes, and an ult that can win or lose games. not only are you responsible for protecting your ad carry in lane, and shutting down the other ad carry, you also have to have a presence in a team fight with often minimal defensive stats, and cc/ skillshots that you cant blindly fire into a team just for the dps. also warding, counterwarding, getting time on things like drag or baron.
i main support, and me and my ad carry run really aggressive lanes. whenever we see a soraka, we can almost always pull a first blood out of her. even though she is an easy champ, positioning, timing, and map awareness, and several other duties stated above are still all vital parts of one of the easier champs in the game.
point; the roles imparts difficulty, even if the champs are easy. sure you can passive lane v a passive lane, and do **** all through your lane except sustain the adc, but then again, is the role easy, or you not reaching it's potential?