Even with how badly the AI plays SoSa, it's still a great card. I had a monodeath deck get to rank 3 in platinum last week, based on poison and SoSas. WillNg got to rank 1 using monodeath rush and SoSas, and he had the highest rating seen in platinum since the first week of the arena. You can't just throw it in any deck and expect it to work, though; it's a tool you need to use in the right situation to be effective. Imagine playing SoSa in a firestall, for instance... oops, there goes all the AIs fire quanta, guess those fire lances and fahrenheits aren't all that scary anymore.
I've been using SoSa in monodeath poison in my bronze league grinder, and I'm finding that the 8hp nerf it was recently given has actually made a big difference. It's still a fantastic card, but the hp loss is significant enough that you need to be careful what decks you play it in and when you play it.