It's an early game meta atm, and so mage supports still dominate because they will usually win lane vs melee supports. Because laning takes up the majority of the game length right now, an adc that's behind has a tough time getting back into the game and mage supports will earn gold regardless of how their adc will do because of the gold income from support items.
Going tanky supports are arguably better in the late game as they can soak up dmg and provide utility/hard cc so that the other members of the team who have more gold/experience can delete the enemy players. To win lane with them though really depends on how you play the lane vs how the enemy support plays the lane. an aggressive mage will win over an aggressive tank because poke>all in. But some tanks have sustain like alistar, so you can win but you have to play the match up smart, like waiting until they're low on mana to engage, or going in once they have their stuff on cd. Personally, this is why I play Taric. Great stun when you want to be aggressive, and a good shield and heal when you need to sit back