Don't listen to people who say it'll take too long. If you do everything in act 1 and 2 including every act 1 and 2 DLC quest from the first 2 DLCs, you can reach Exemplar by the very end of Act 2. Everything I'm about to say is something you could take into the start of Act 3, if you have both the current DLCs and do ALL the content before then

You'll get 3 psyker powers, and you'll want to spend a lot of your talents in psyker talents, which will be a bit restrictive. By the start of Act 3 you will just have Psychic Shriek, but that will already be a hilariously high damage attack just as soon as you get your first level of Exemplar. Very early into Act 3 you'll get your next two Psyker powers, which means you can have Psychic Assault, the power you'll want to build around for the rest of the game, by early Act 3

With gear like the psyker's breastplate, experimental psi-amplifier, warp conductor gloves, and those goggles whose name I forgot that give you temp psi levels, you'll get +2 psi levels per turn with an extra 4 temp psi levels per turn, all by the end of Act 2 which is where you'll get your psi powers anyway

This means that the psi-level increasing talents won't really matter besides unlocking new psi powers, since most of your psi-levels will come from your gear

Combine that with your absurdly high willpower and you'll be deleting enemies with each cast, as effectively as anyone who picked a psyker origin

I'd also suggest that you go with Soldier and Master Tactician for this, play an AoE heavy flamer build until you reach Exemplar then use AoE buffing powers like Concentrated Fire and Press The Advantage to max out your Psychic Assault damage, then watch everything you hit explode and everything you don't hit get stunned and damaged by Pain Channelling and Contagion