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

There are three main squads in my shard. The one mentioned by op, GK-zarris, and aa-hoda. Some people use Rex for lead and drop someone else. There are some nightsisters too. The biggest issue is defense. Most people use one of those three squads so they don't move in arena much. I use CLS, Han, r2, and Wiggs. They take those down easily but they also don't hold you as well as the other squads.