Not sure if I'd agree with you, I'm afraid. To me, a "meta" is defined by popularity, or champions that would be considered over-tuned (whether directly as a result of their kit or an item they would use as a core item arguably being too strong). Just because you play a champion that doesn't benefit from either of the above scenarios, does NOT mean they cannot be competitive at any given role.
Every champion has risks of ks or minion kill; but I'm not entirely sure why you base kill-power as an argument against a champion being played as support. I would argue that Teemo is great bot-lane due to his blind, esp. vs. ADC's who have power built into AA empowerment (such as Draven & Vayne, etc). Also, where do you think shrooms are being placed? Any Teemo who puts shrooms in a middle of a lane are doing it wrong, in my opinion. When used properly, teemo shrooms can be used for some pretty amazing map & objective control. The meta currently favors more ranged ADCs (Varus, etc) so I could understand an argument such as this vs champion like Teemo, but not any of the reasons you noted.
I don't have advice for your own perception of certain champions. It sucks that there is a certain stigma in League that erects when player's choose champions in a given role, and that shouldn't be a dictator as to how the game will go. Especially if the support is trying to communicate to the team and is comfortable with their pick.
To me, supporting is a state-of-mind, a build of items, a tool of utility, and is a style of play that allows for decision making, anticipation, prediction and ward-control to shine. Are certain champions better vs. certain picks? Yes, but that doesn't mean we shouldn't be allowed to, or flamed, for playing a champion that you (or anyone else) deems as "off-off-meta".
Note: this post does not justify the behavior of any individual who purposely trolls, plays irresponsibly or cripples their teammates because of their unfavorable playstyle. If you have a support who buys a sighstone, contributes to the teams utility and continues to play their best while playing an "off-meta" champion, don't complain and tilt the team with your stigmatized self-doubt. Maybe try adjusting your frame of view, magical things may happen.
[slayer-jinx-catface]