Hello... I'm posting a lot, I realize. Anyhow.

I've got an astropath player who's taken the 200xp "I'm a custom mutant" route, where his psy rating is increased by 1, and he gets 2 free powers. He's used the four free powers to buy Delude -> Compel -> Sensory Deprivation -> Dominate, in something of a "technique steamroller". I'm wondering if this is completely legit, or if he's just found a shortcut, at the cost of having to work hard to gain other powers later?

I'd slap my players upside the head for coming up with it, then allow it provided they came up with a good explanation for how they managed to hide their extra psychic potential from the Adeptus Astra Telepathica. By the Rules as Written, it's completely legal. So long as they meet the requisite powers, they can take any power from a Discipline of their choosing.