User blog comment:Bashfrog/Apc Supports- Cause You Can/@comment-1330314-20130807153302

While a lot of supports are sort of viable mid, ultimately they're far more effective when building as an actual support. Even though the above are scary powerful when played AP, they're more efficient with cooldown reduction, which is cheaper to obtain. Their main strength also tends to lie in the utility they give and not the scalings, so they still remain strong even without building damage. The other problem lies with their lack of burst: most AP mids are capable of dealing a lot of damage instantly, whereas champions like Soraka and Sona can only deal the same amount over time. The ADC also still needs a support close by in any case, so laning mid or top would just mean they'd need another support champ, whereas laning bot would seriously hamper their own carrying ability.