Been looking into a Nurgle Sorcerer recently myself.
I've noticed a lot of folks attributing skills/talents/powers to the gods incorrectly.
Tzeentch has a lot of the psyker goodies (Will Power, Psyniscience, etc...)
But not ALL: Psy Rating is Unaligned (as are Child of the Warp & Sacrifice)
Lurking about here I've read some posts where people attribute the powers themselves to Tzeentch
The "base" powers/disciplines (Telepathy, Telekinesis, Divination, Biomancy, Pyromancy) aren't aligned
Nor of course the ones under "Unaligned Powers"
The Aligned powers count towards your alignment
But you've got to be aligned to buy them in the first place as they list 'Aligned to X' or 'Mark of X' as prereqs
All except "Acquiescence" pg.217 Core BC
Which has 'Devoted to Slaanesh' as a prereq... which is probably an editing error
(Unless it refers to the obscure mention of Devoted on pg.84 Core BC: If a character ever has three more Advances that are associated with a specific Ruinous Power than any other, then they are said to be Devoted to that Dark God... which is itself probably an editing error as everywhere else it says 5)
I've also seen confusion about Marks of Chaos being granted by advances
Its explained on pg.78/82 Core BC
When you have 20 advances to a particular god, and at least 5 more to that one than any other, you get your Mark
tl,dr: Not all the psyker goodies are Tzeentch's