I don't know much about fighting games (I'd like to change that though!), but from my experience with games like League of Legends there's always flavor of the month characters which people flock to because they're the best, after a while the metagame gets broken by some intrepid group of people and everyone flocks over to a new corner of the room. I'm not sure to what degree fighting games are dynamically balanced (I imagine not), but it certainly helps to facilitate a shifting metagame as opposed to a strict list of tiers.