I’m on server 8 so I don’t know if this has changed at all on others, but there seems to be some really serious balancing issues. If you’re going to have a big roster of characters that keeps expanding, they shouldn’t be made redundant by frankly overpowered characters. Violet is the main example but Sully is a big issue too, both of them bringing a massive defense which can either run down the clock or allow damage heroes to wipe out the other team. This is really evident in the arena where you can see literally dozens of teams that have the same characters over and over again, because there’s not enough reason not to use them.
Characters only seem overpowered in the early/mid game. Once you have a large roster all skilled up at max level, things are a lot more balanced. Sure there are some characters that will always lose to certain others, but that is balance as those are that characters counters.
Certain comps will run arena for a week or 2 until one person figures out the counter comp to that team. Once the counter is known, everyone will change their teams.
I really expected you to be posting about Tia lol. Sully and violet are not troublesome at all and are balanced just fine.
You can counter violet with rex 
It does not matter how well a team works together in arena they should not beat a team twice their power level and the highest one 9 levels lower than the one team. I just lost to a 25000 power team and mine was 52000+