Gragas is Annie But better
With the recent Changes to Gragas and his Q we have a tank-esque mage support who has a good stun (e) a strong slow (q) and an aa steroid (w) as well as sustain while in lane(passive). Then once you hit Post 6 you have a displace/knockup to make Janna go," Oh DAMN". So in review; Annie: Q high magic damage single target point and click, W Armor/MR buff but no damage prevention, E AOE cone Damage spell (commonly used for stun), R TIBBERS (neat controllable) DOT pet that is good for taking Tower shots while minions show up also solid Stun initiate. Annie has Low mobility without Mobiboots and has a Stun that telegraphs so hard you have to burn flash to get close if you prep it. If behind Annie is just another back line who now has no burst and can only Disengage.
FatMan: Q VERY strong Slow combined with high scaling AP burst, W Ad steroid for single attack again scaling AP, E Strong low cooldown single target stun/gapcloser/escape. R Huge AOE disrupt/knockback(up) that deals solid damage. Gragas has some solid health and scaling ability as well as even if he gets punished hard bot lane he can still poke/slow and displace later in game. Fight In drag/Baron pit Graggy Ult, Enemy team chasing hard and adc/apc out of position get separated and nuked. More utility, sustain from passive, Caught out warding Does Not = dead and solid wave clear when fast pushing.
Graggy is better across the board.
Just my opinion, feel free to hit me up if you have contention.