Hmm the pet does what's listed, 3secs recast 90potency is a 75potency "normal" cast of 2.5recast, or you can count it as a 90potency dot. Regardless, it does solid damage, not counting the special attacks which have too long cds to really matter. I pointed out before that I tested it and as far as I could tell, it does work exactly as if you were casting the spells, his 90 potency=your 90 potency. His stats are however generated on summon and he needs to be resummoned for stuff to update properly when you swap a weapon, but just looking at the numbers he certainly does slightly more than Ruin, which is how it should be, but casts a bit slower.
On the CNJ ACN stuff, I've lvled CNJ and ACN to 20, lvled CNJ to 24 last phase, and it's very obvious to me that ACN solos a fuckton faster. The fact that I kill mobs in ~4casts, they don't die on the 4th cast since it's dots, but that's all I need to cast to kill a mob, means it's naturally going to be faster than CNJ, regardless of what you're doing and how much dmg per cast you do. I don't cast Ruin much when soloing, only when I want to drop a mob quicker, I mostly just dot shit and run around while they die, pulling the next mobs in the mean time. Oh also you can grind forever as an ACN, as a CNJ you have to take mana breaks every now and then because the mana efficiency is poor and the only mana regen tool you get is at 34 or 36, and I don't even know if it'll be enough.