I just tried a tower build vs normal AI and was out leveling the computer quite a bit. I had some items that reduced my cooldown and was able to get 5 towers up at once.
I wouldn't call the towers unspectacular. I was doing pretty well with my first attempt at a tower build. I finished the game in 14 minutes with this build. No hammer slam or rook roll. Just towers, struct xfer, and stats. Got lots of armor items too. Due to the suicidal AI they were dropping like flies.
I am going to give it another whirl and try harder AI this time.
20 Minutes vs all Nightmare AI. Only died because I was on the phone. I think the towers are probably good.