Alright, I get it, the devs have way bigger fish to fry, and costumes/costume brawling are basically an abandoned limb of content that really only get used a couple of weeks a year during Halloween...
...That said, EVERY year this stuff bothers me so I figure I might as well say something and see if the festivals team takes note and does anything. Probably all of these issues have been known and reported for years, but:
The biggest issue isn't really a bug, but it's very well known that a couple of the toys have just grossly disproportionate power to dominate the brawl. After MKS (which is the easiest time to try to rack up a few brawl wins) if one or two people have the axe toy they can effectively stop everyone else from ever winning as long as they want to. The boxing gloves can be pretty bad too, but the axe is by far the worst. In years past some people would hang out at the forge to deliberately troll people trying to trade for the dailies, but I've seen less of that fortunately.
Any of the costume brawl skills that inflict daze also put your character in combat, resulting in you being unable to use any skills until another brawler hits you or you manually re-enter the brawl.
The behavior of the hit stacks is either bugged or extremely punishing. If you get knocked out, you lose some (all?) of your hit stacks, making you have to start all over again. It's almost unavoidable to get knocked out (see point 1 above), so simply making it so that hit stacks can only increase would make it fairer and more fun.
It used to be that you could easily rack up 10-20 "wins" in the MKS mosh pit, and that was really fun and a simple way to bump up your brawler achievement in a non-grindy way. Now that's pretty much impossible without the axe toy, given the issues above. I hope they could take a little pass at this before next Halloween, or maybe throw Costume Brawling back into the dailies. Nobody wants to brawl anymore and that's kinda sad.