Why is Gragas used so much in competitive play?
Been watching a lot of competitive play lately on youtube and I've noticed that Gragas is picked in every game by one of the two teams playing each other. However, he is listed as an E tier pick with a win rate of only 47.86%, and a ban rate of only 0.34%. So he doesn't seem to be doing very well, and clearly not well enough to use a ban on.
So, what makes Gragas viable at the very top of the food chain, but seemingly completely useless in any type of play below that level?
Edit: Thanks for all the replies to this, I have a better understanding now.