Guehlfirf's metathermics build has a few flaws like lacking fancy footwork and onslaught, I would recommend going something like this instead:
https://underrail.info/build/?FAUNBwMDCAYAAwBuKAAYTywkAEVYDTQ8AABuRgAAUiY5KyzCjBIqZRM8wo3ChwbfvwYour psi slots at level 20 on this build should be cryo orb, cryostasis, cryokinesis, LTI and PTC.
When you acquire stasis replace cryostasis or cryokinesis with it. Psionic mania + premeditation and cryokinesis/cryo orb gives you some strong ranged options with the latter also letting you proc TFB and opportunist on the survivors, I would not recommend slotting in thermoD on a build like this since you are a melee, though you could use it along with pyrokinesis for big crowd control damage combined with psionic mania.
EDIT: PK build:
https://underrail.info/build/?FA0GBwMDBwYAAwBuKAAYXUcwAEpZADwAAG4ARgAAWCY5Kz_CjBIqE2nCjWjChxTfvwSlots should be contraction, lti, proxy, tk punch and electrokinesis early on, later stasis.
This build trades off raw nuking power (from Psionic Mania) in exchange for crowd control and quite a few disables (5 ap proxy undulation, 10 ap tk punch, 0 ap electrokinesis from premeditation) I would recommend speccing undulation after flurry ap cost and cooldown. Also you should take taste for blood later on, after you join the Free Drones.