Ideally, a fighting game doesn't have tiers. In actuality, that's almost never the case. While you can with with pretty much any character, especially in Brawlhalla, there are clear-cut differences that put certain characters on top at high-level play. In games like Brawlhalla and Smash, this usually comes down to speed. The best example I can give is Super Smash Bros. Melee, as someone who is deep into the competitive community of that game. If you look at the top 7 characters in that game, they're pretty much the fastest characters in the game. Fox, Falco, Marth, Sheik, Captain Falcon... the only exceptions are Puff and Peach. Similarly, inn Brawlhalla, speed seems to be the biggest factor. Since this game isn't as combo-heavy as Melee, it makes it even harder for slower characters to have a chance, since they have a hard time punishing in comparison. That's why you see characters like Hattori and Asuri do so well in Ranked. Their attacks come out fast and have low end lag. As someone in the lower mid levels of Gold ranked Brawlhalla at the moment, I can attest that fast characters are definitely the hardest to deal with in high-ish level play, at least from my experience. If you play a slower character, not only are you more vulnerable after you attack (due to higher end lag), but you also have a harder time punishing a faster character (Due to your slow startup on attacks and their low endlag.) In Brawlhalla, strong attacks mean a lot, as they're your best kill option, and characters with quick strong attacks seem to have an advantage at the current point in development. Again, that's not to say that you can't win with slower characters, but it requires a more read-based style of play, which is just more difficult to do consistently at higher levels.
Tl;dr Brawlhalla will probably have a tier list at some point, as most fighting games do. I imagine faster characters will be near the top, basing things just from my experiences. That being said, I do think the game is fairly balanced, though certain characters could use some tweaks to give slower characters a more even playing field. (Also I think dodging could use a nerf... It refreshes a bit too fast as is a bit too difficult to punish the way it is now.)