I continue to have total party wipes despite not having problems on the normal game.

I would appreciate any tips/strategy to survive against the captain. It seems there are some real trade offs on the various buffs and also on aiding the spirits or not, but none of the combos I've tried have succeeded. The fear effect in particular seems to deny my party the chance to succeed.

Thanks!

You probably mean the "Anomalous signal" missions.

Well, playing on Hardcore diff, I wasn't having problems during this awesome mission - albeit, I was using Force Psyker and "Purity Prism" skill, that practically negates all in-battle debuffs and even causes some of them to manifest on enemies.

TBH, Despite having (literally) hundreds hours in the game, I don't think it is possible to have much success with harder missions (normal runs apart from normal/cakewalk) or more challenging story ones without Force Psyker's protection from debuffs. Some of them - like poison, bleeding, etc - can wipe your team in a round or two.

Sure, high-lvl Soldier can tank the damage and heal, thanks to "tactican" tree (leftmost one) - but no one is wise to tell how to reach that level without protection during earlier missions.