It's true that jtr teams are better than cls teams given same mods but cls is bit more flexible in that he doesnt necessarily need to be leader.
What's better is his tm gain. When he doesnt have 'call to action' buff (i rarely use that buff when i'm on offense in arena these days), he gain 10% tm whenever a rebel ally is damaged. Now palpatine does some damage to rebel allies whenever rebel ally takes a turn. And I use Han solo. So cls is guranteed to gain tm from han, some more from r2.
Even better, he feeds tm to all allies when he scores a debuff
In short, cls can contribute more when you fight a meta team(with very good mods) on offense (palpa, traya, sion, vader/thrawn, nihilus all zeta)
Yes when you go against easier teams rjt can just hit auto. Cls needs control. But still that doesnt mean he cant beat
Also i can make a makeshift rex team and put cls in the lineup when i go up against hyper fast rex lead palp talzin gk thrawn team