Psi Sniper hybrid is one of the most powerful class in the game. OP you are correct the lack of defensive skills and three psi school are detrimental.
I cleared version 1.0.2 hard w/ the following psi sniper build:
http://underrail.info.tm/build/?AwGloJgVhGDYQHYQGYQEYFoelMXhhHoRq4yGECcAHBuqInTVRsBEQCwzlGHogODQR2iosdTh05ooAqLPhpEyqEAYou might raise your eyebrow at 3 WIL, but hear me out:
At 3 WIL, thought control psi skills are now a gamble. Late game enemies will resist your thought control when you need it the most, so thought skill = 0
You need 25 Psychokinesis for Force field, 30 for Electrokinesis, and 45 Electrokinetic Imprint. You don't care about the damage output from these abilities as you will use them for crowd control. 3 WIL = perfectly fine.
At max level, max Metathermics and 3 WIL, Thermodynamic destabilization (ThermD) = 189% of target's HP <- this is good enough, therefore you don't need to pump WIL.
ThermD is the bread and butter for this build. Snipe kill straggler from stealth, premediation ThermD the enemy w/ the highest hp near the center of the group; aimed shot kill ThermD enemy -> BOOM -> if need, adrenaline, toss a high grade frag grenade -> most of the time battle over.
If you want to try out my psi sniper build, please keep in mind version 1.0.3 changed junkyard surprise so it no longer offer +2 INT buff. You will need to adjust crafting skills accordingly.
You can find skill check thresholds and crafting skill requirements from my faq:
https://steamcommunity.com/sharedfiles/filedetails/?id=843557165I heard you can also do a thought control sniper hybrid. I can't comment on that build as I don't have any personal experience w/ it.