Skills for an Inferno hero.

What's the problem with holding out for one turn until the gates open? Is defense absolutely necessary, taking up an entire slot? And besides, a slight reduction in damage isn't that significant; I'd say it only marginally reduces the damage received from archers and fast-moving enemy units. Moreover, it's often more useful to not summon Cerberuses and Unicorns, but to attack instead, as speed and initiative allow. Especially if the Cerberus is an alternate unit, and the enemy has gathered their troops in a formation, as they always do, protecting their archers. And also to break the formation with Nightmares and immediately reduce the number of the enemy's most dangerous unit. Of course, this is if it's a final battle. If it's a simple, routine battle, then, of course, you need to open the gates. But even here, defense isn't critical and plays an even smaller role.
That's what I think.
As for Chaos... I don't know. A Warlock is a Warlock, but such a Chaos unit will only be effective at the beginning, clearing out creeps. In the late game, it won't be decisive at all.