Gragas is mid T1 according to Elementz.
I wouldn't place the entire world into Elementz's view point, but generally speaking if he says a character is strong it's probably pretty strong. Note that he also does it in terms of the current 1-1-2-1 meta and dragon control etc (that is, Shyvana isn't a weak "character" by any means, but her lack of CC makes her a mediocre ganker, and soltop she can be shutdown by a lot of people. So even though she's reasonably powerful and might work great if the meta were different she's 'bottom tier' anyway).
* Tier 1: Xerath, Rammus, Kog'Maw, Irelia, Cassiopeia, Skarner, Udyr, Morgana, Ryze, Karthus, Zilean, Galio, Gragas, Tristana, Sona, Cho’Gath, Vayne, Kassadin, Yorick, Alistar,
* Tier 2: Kennen, Caitlyn, Twisted Fate, Graves, Rumble, Anivia, Lee Sin, Nasus, Amumu, Fizz, Brand, Riven, Ashe, Trundle, Maokai, Wukong, Gangplank, Ezreal, Urgot, Annie, Janna, Sion,
* Tier 3: Akali, Nocturne, Tryndamere, Renekton, Fiddlesticks, Swain, Jarvan IV, Heimerdinger, Singed, Corki, Shaco,Orianna, Miss Fortune, Taric, Jax, Mal'zahar, Teemo, Talon,
* Tier 4: Veigar, Lux, Blitzcrank, Shen, Vladimir,Warwick, Olaf, Xin, Zhao, Garen, Nidalee, Leona, Kayle, Poppy, Soraka,
* Tier 5: Leblanc, Malphite, Nunu, Sivir, Pantheon, Yi,
* Hard to place on a team: Shyvana,Twitch, Mundo, Karma, Katarina, Eve, Mordekaiser
I mean, Leblanc was kicking ass in the tourney and supposedly T5 P: