Off-Meta builds are fun and all, but they are supposed to be Off-Meta. [MAGE SUPPORTS]
The fun thing about an Off-Meta build or champ is how weird it is. No one ever expects a banana top lane.
But the issue is with people loving weird things 
ADC for example. Riot lets them happen because people like diversity. But when Ziggs starts getting balanced around Mid AND ADC, it not only makes balancing harder. But have large ramifications as well.
This post isnt about Ziggs ADC though. Its about champs like 
and while MF isnt a mage support she still fits the build of an Off-Meta pick becoming Meta.
Riot starts to take Off-Meta into consideration when balancing and they shouldn't. If it is supposed to be an off the wall tactic no one expects, if they consider it, it isnt weird anymore. Because it is popular enough to get attention.
And while Metas can change with Off-Meta strats, they need to CHANGE not just increase. There always have to be a Meta or the game would be physically impossible to balance. And every type of champion should be viable at any time.
Right now though classic supports are getting far FAR outclassed by mages. And Riot is balancing these mages so they can work there, when they arent supposed to.
Mages can still go support, but it shouldnt be expected, ranged champs can still go top but it shouldnt be expected. And no class should hold dominion over many lanes, while one gets none.
support is good and her best role
because they can just use their spells to poke from range without having to worry about conserving mana for csing, and they are safer from ganks because there are 2 people in the lane.
The other reason is because traditional supports are reliant on their teammates, cannot carry or do damage on their own. They are not as fun to play, as many support mains would agree, and is further proven by autofill. Autofill is another big reason for offmeta supports gaining popularity. People unfamilar with support forced to play the role.