CLS came out, along with his buddy R2, and the Zaul meta ended. Not because it wasn't a viable or useful team, but because other teams were more obtainable, or easier to mod, or any other reason.
Zaul teams are still a challenge for most lineups that don't include CLS, R2, RJT.....They make excellent defenders in TW, are needed for TB platoons, and can excel in later TB missions where other dark side teams can't.
Arena is the one place that they don't shine but not because they can't win on offense. It is because everyone knows how to easily beat them and the current top "meta" teams are designed perfectly to do so. Therefore, you fall further each day then those who run those "meta" teams making it more difficult to climb each day. You net less crystals, either because of lower PO rank or because you have to spend for extra attacks, causing the ROI for arena efforts to decrease forcing you to face the dilemma of "Can't beat em, join em" or accepting that you will put yourself on a slower path to growth.
All about how you want to interact with the game. If insistent on NOT chasing the meta, you have to understand that you are putting yourself at a strategic disadvantage to those that do. You can be just as successful but the effort required to achieve it will most likely be greater and generally be at a decreased value than other players
