I find RG to be quite useful in some cases to save Emperor from an iminent death and to be an extra Stun/Speed Down.
It depends really on who you face in arena. If you need a taunt at start to avoid the AI to kill Emperor before his first move, then Shore. At 3* he is good as long as you gear him enough to give him protection, and fill him with a lot of extra health+protection on bonus sets and secondaries.
RG is becoming "obsolete" for arena with the newer tanks, but he is still good IMO in other game modes besides arena like AAT Raid P3 or GW.
