there are only few who main support so the most supports are really crappy xD
i main support in low elo (top elo 1500) and i am very pleased with my elo because 1500 elo is too much compared to my skills x) anyway even though i am worse then a lot other players i am a better support then the most other players at my elo. so imagine ur 4 team mates and 4 enemys have the same skill BUT u are the supporter and u are better then the enemys supporter. if u rly main support its most likely that u are far better then the enemys supporter xD ur entire team will have an huge advantage.
(sry for my bad english >_>)