All of the below is for unupped play only.
Burst strategies are already a way to beat SoSac. Bursting your opponent below 48 before they expect it is already a way to make all future sosacs useless without healing. SoSac is not overpowered - in fact, it's quite underpowered. It's useless in monodeath, far worse than bone wall. The only deck where it can possibly be used in is death pendulum splashing it into monolight stall.
I have to completely disagree that its counters are too situational. Purify, perhaps, although healing for +2/turn for 2
is bad but not useless. SoP is not situational at all. And the major way to beat SoSac is through smart play such that they can't chain it. Keeping damage back for a burst, RTing/AMing/CCing your own creatures. SoSac is one of those very few cards in EtG that actually reward someone for their play skill.
SoSac does not need another counter, is not overpowered, and its counters are not situational. I do not understand why it would need such a nerf.