Squirrels are a pain, but at the same time I'm not sure they ever intended that the win streaks would be as long as they are. At some point you aren't suppose to be able to beat it by design. The crazed rodents may be the way they are addressing that.
That said, I've had good luck using Ninja to turn them around. My all purpose Temple team is Plant, Ninja, Thief, Cyclops and Bard. I'm not getting through the higher level lines without casualties but I am getting through. S5 with decent gear, runes and legendaries which also helps.