There are two main configurations of a Rex lead that are nasty and efficient:
- Rex, r2, Chaze + 1 (DN/Thrawn)
- Rex, r2, GK, + 2 (Raid Han, DN, Thrawn)
On the younger shards, DN is the main threat. So if you dont have a supporting cast, rex is a bad idea.
Wedge and biggs are excellent on younger shards, but as you see, you need an uber autotaunt tank, which will be either GK or Chaze. Old ben is ok too, and viable end game, but not quite as deadly.
As more rex leads pop up in your shard, which they will until CLS/JTR events come back, you will start to struggle until you get Chaze or GK for yourself.