I suspect what most of you are complaining about is not zMaul but rather herd mentality among players. We always have these phases where there is a nice squad or character and everybody seems to jump on the bandwagon. Just wait a short while and the picture will soon shift to something else or people will discover a variety of other squads they like better.
For what it's worth, on my soft-launch shard the majority of top-twenty arena teams are now Rex leads - it was 16/20 when I was playing last night, and one of the other four is Nihilus lead - this change happened in the last two or three days and it suddenly spread yesterday. People will tend to follow the current fashion until they get more familiar with the options and make their own choice.
Leave it alone, it's all fine. No need to call for knee-jerk reactions to "fix" whatever you are seeing in arena at the moment. It is self-balancing as players will always migrate towards counters to the prevalent teams, sooner or later, and then to new formations nobody thought about before. The META always shifts and evolves, and it does not require any changes or new characters.