Hello Dane. I like your idea as a possibility to have viable psy lore outside of telepathy and biomancy.
However:
1) the Primaris, may better not to tie it to Toughness because it benefits mark of Nurgle models more, and it's already the best of all marks
2d6 t4-tests is 4.62 wounds average and t5+ tests 5.83 wounds if my math isnt wrong
2) Weapons of corruption look really complicated, may be just rending for
cc and ranged attacks,
CSM don't have much rending in the codex (
DP of Slaanesh only
iirc)
it's simplier and effective against
MCs, imagine berzerkers getting that (if only could they reach combat..)
3) Cursed land resembles Cursed ground from malefic, what about
Wreathing landscape - Conjuration, 1 Warp charge: place a 0" marker anywhere within 24" of Psyker for duration of the power.
All enemy units treat area within 9" of marker as dangerous terrain, but friendly units count it as open ground (now Possessed and Warp talons can have a chance to strike at initiative).
4) Wake the Warp - I like that spell idea but removing with no saves is a bit much. It can be funny to remove those Riptide wings though