The meta of League of Legends seems to be shifting, instead of using for example: Nami, Lulu and Soraka as supports, people is using Annie, Zyra and others to fill the role.
When one uses such characters in the bot lane, are they really in the support role? Most of these supports have full AP builds. For me, they're not really supports, for me it seems that they're just using mages in the bot lane.
I guess that people is calling such characters as supports just because tradition, and then independent of what you put in the bot lane, it's going to be called a support. I believe that in RPG games, a support is a character that is completely diffent of, say, Annie and Zyra. And also that the idea of supporting comes from there.
What I don't agree is that they're being called supports. It's like if the word support is being used as a synonym to companion. I believe support is a class of characters that have a pattern of skills for helping in a specific way, and not helping in all ways.
Best Answer
The question is hard to answer, mostly because the notion of supporting is vague. There is no clear definition of it when it comes to the game itself. Also, you cannot apply the terminology of another type of game. Since their is now particular definition for the game, I can only respond to the question based on the dictionary.
Dictionary will say that supporting is "to act in a secondary or subordinate role to (a leading performer)". With this definition, Annie, or Zyra can be used to support an AD Carry. Their main function is not to provide a burst of damage, like they would do as midlaners, but to be able to reliably control the enemies by landing stuns or root.
Of course they will build more like mages in the end game, mostly because their kit benefits from AP more than other stats. But traditional supports tends to do as well now: Lulu shield, speed boost or slow also scales on AP.
Furthermore, itemisation of such supports will strongly vary from a mage build. They will more probably go for utility first, with Sightstone for Warding and Cooldown Reduction to ensure they can get more stuns and root.
As a conclusion, I think that supporting is not depending on champion (even if most champion would be weak supports). Support in League of Legend is a role, it is not a category of champion. For being a support, you need to be able to provide for your carry. That can be : crowd control, sustain, protection or maybe other things. In my opinion, the meta has not changed yet. Gamestyle, however, has.