RG is better then sun fac. I run AA Leia Rex QGJ sun fac. Used to be RG but couldn't get past the RG+STH+Rey meta.
Sun facs taunt got fixed but he follows up with ability 3 instead of basic which is useless early game so you don't see dispels until round three where a Rey team will have two players down by then. When he's stunned he's useless obviously and Rex won't give him immunity until round 2 so a simple dispel of his taunt or a stun in round 2 makes him a weak damage liability character. If the AI gets fixed and he starts basic attack round two he will be better, mainly for the dispel, but right now RG and STH are better. Once the ai is fixed he might surpass STH but RG is still meta tank