Sunder Soul needs a bit more boost.
Sunder Soul us a nice ERE but it is underperforming compared to others. So it's one more reasn why it is barely used or not used at all.
It should be able to do same damage as Deconstruct (which is also a similar ERE).
I've tested Sunder Soul a lot with few different builds and the most damage in PvP a was able to do was around 900-1000 max.
While with Deconstruct you're able to do like 1.5k up to 2k in PvP maybe even more.