I think the issue is that CLS along with gXII bring tremendous imbalance for arena the way it is currently devised which leads to the idea he's too OP.
Since arena is dependent upon age of shard, CLS rules the day easily in younger shards but in an older shard especially nov/dec 2015 he's on almost every team in the top 100 which means he's less valuable there and more of a requirement.
Where he really shines is in raids and GW, I believe in 6 months when he's come around again he will still be a top toon but no longer OP because other toons will get boosts from gXII to even out