He likely is, or at least almost at that peak. Remember, Argus' WORLD SOUL has been tortured and fucked up by the Fel for ages now. At this rate, Fel Magics might not even affect him.
Also, OP, Argus is NOT in Avatar form when we fight him. He might just be the only Titan that can change sizes. Likely the reason for as to why the Titan's found Azeroth first, and not Argus. Argus might've had cloaking feats not even the Pantheon could notice. Hell, even when Sargeras WENT to Argus, he didn't know that a Titan was in it, until the very last second. Hell, Sargeras thought this Titan to be SO useful, that not only did he use his might to help him with his infinite army, but he's pretty much Sargeras' Ace in the Hole card.