He’s fine as a tank for a rainbow team (I’d describe him as good but not great). Doubling up colors is very dangerous on a defense in general.
Bear in mind, though, that a tank really succeeds or fails based on the team around them. Anzogh needs fast heroes to convert his AoE attack/heal into kills.
Counter-intuitive as it seems, he also really needs a crit troop rather than a mana troop. He has a high defense but low health, so his defense needs to be boosted as high as possible in order maximize the chance that he fires. No matter what, he’s a 3 tile kill for a 5* mono team unless he gets an attack off.