The whole arena is a joke. I'm a new player and can't even get out of the starting block in Bronze I because every player has their team of Epic and Legendary maxed out and assended. There's no reason to start playing.
The only way to fix it is to place restrictions of what can be used for each tier.
For example:
- Bronze I you can only use 1 Rare (Leader) and Commons.
- Bronze II you can only use 1-2 Rare, Uncommons and Commons.
- Bronze III you can use 1-3 Rares, Uncommons and Commons.
and so on.
Doing this shouldn't be too hard update to do to fix the balance issues.