If you take the Mystic role you get to be a psyker without having to post for the elite advance. But the elite advance also says you need 40 willpower; how likely are you going to be to have rolled that well during character generation (the opportunity to spend xp comes later so you can't use that).
Furthermore the powers have a bunch of perquisites, such as certain characteristic or skill scores which may have nothing otherwise to do with bring a psyker.
Isn't this really needlessly convoluted?