Brawlers feel a bit clunky right now, not very snappy. This is down to their mettle system and the slow attack speed (animation times themselves are probably fine apart from buffs but there's an annoying delay between skills it seems
These suggestions come with the assumption in mind that the current brawler bugs are already stamped out, all the skills and traits work as intended

Let's get right to it...
-Faster attack speed in general or a reduced cooldown on the attack speed buff
--0 mettle for interrupt and half the base cooldown This is probably the easiest and most effective thing you can do to help brawlers in their rotation (so when traited it's 10 seconds, they could honestly afford to make it like eye gouge for wargs and reduce the cooldown further, then you could animate cut things more consistently and can feed more interrupts and attacks in your rotation, would just make for better gameplay)
-Just. More. Damage. They're still undertuned. But also...
-Brawlers currently have no bleeds, unless they're going to rely on a consistent, very heavy attack to finish off a mob, they need some sort of bleed, passive or active. They are the only class with no bleeds
-The gameplay of brawlers are clunky and slow compared to a champion or guardian, interrupts would help but reducing mettle costs for some of the skills would also help considerably more. 3 mettle for every skill right now, some of the mettle spenders are simply not strong enough to warrent spending 3 mettle when cooldowns overall are fairly low
-Better traits for yellow, they're almost all underwhelming also they should ideally cost 1 trait point, not 2, I can't see many reasons why you're going to trait all the way into yellow for the capstones.
-Buff skills should have faster animations or be immediate, there are quite a few buffs for both lines and I see myself running around a mob doing the same animation 3 or 4 times before I attack again :/
-Pummel attacks way too slow, not sure if this is an engine issue but it would be so cool if with each punch you actually saw a hit number and an attack, it would be a bunch of less powerful but far quicker attacks and I think just aesthetically it would be cool to see.

I hate to say it, but brawlers in their current state are underwhelming... They lack the snappy, satisfying gameplay that they were trying to go for and I think the high mettle cost and slow attack speed is to blame. Balance and general stats aside, you want people sticking with the class, they need to have something special about them... They're *not* filling any unique role, other classes can do dps and tanking, so really when it boils down to it brawlers are champions without weapons or yellow line. It's fine to have them just be another 'into the fray' type melee class. I like brawlers as a concept, I like the idea of a hard hitting fist fighter but they need to be satisfying to play, it's all there to be a fun, satisfying class, they just need some adjustments.