What does it mean when all the teams are the same in Arena?

I go and look at my shard and the teams all consist of CLS, Raid Han, Thrawn, R2 and GK. I go and look at the meta report and everyone is using those same toons. Looks like diversity is frowned upon in Arena and only overpowered Legendary and Raid characters are being used.

Why is CG not focusing on diversity in their game and only making a few characters overpowered and more viable than the rest?