Just tested on beta. Confirmed that ER bonuses are not applying, leaving my max level character at CL40 instead of 50 for stormsongs.
I think Great Thunderstrike should be 2d8/CL (900 at CL50) instead of 2d12/CL (1,300 at CL50). Adding a 10 round blind effect to Thunderstrike and Great Thunderstrike would make them both more useful as disables.
Great Thunderstrike has lost that additional 3rd strike, but still remains a line for targeting, although it doesn't hit anything if fired that way.
The VFX and spell icon for the default Winter's Ballard (Call Lightning Storm) is much more impressive than Call Lightning. Perhaps Stormsong (Call Lightning) can take the Call Lightning Storm VFX once Winter's Ballard gets changed into a Chain Lightning effect? The Winter's Ballard icon should also be changed to the one for Chain Lightning to reduce confusion.
I have not tested if the stormsongs work with the epic purist caster feats (Domineering, Explosive, Harsh), but ideally they should not - otherwise, purist casters get a pretty huge advantage over other classes like Bards, Warlocks who can take stormsinger. The base numbers of the stormsongs are calibrated to match the output of a purist caster with identical CL anyway.