I found PSI to be underwhelming given the hype I heard. They are slightly more powerful than any of the base classes, but I don't think they are nearly powerful enough to justify a strategy where you push any early resources into PSI, given the time and money it takes to cook one up. And by the time you hit end game, your base classes are so strong it's really not massive.
Honestly, I think PSI would actually be helped a lot by being 'random' (Which is odd because they made everything else in the game very random. but then made this consistent). Make it much cheaper to get Psi training set up, and slightly quicker to train than now. (I would recommend that going on missions rushes the current training, maybe a mission knocks of a day, plus a few hours per skill used in the field)...BUT make it so Psi Talent is only discovered at Sgt+ of a normal rank, and somewhat rare. So you have to give up a decently trained soldier already and if you want Psi you have to rotate soldiers more regularly. (So a hybrid of EW Psi+Mech soldiers, you give up a soldier to get a Psi soldier. Maybe even have small bonuses depending on the class+rank of the soldier you gave up, like Psi Snipers would have a special Psionic Shot, and Rangers can Psi-Conceal for a couple turns heh.)
This way it's like getting special items in the foundry; if you get lucky and get a Psi soldier, it's a path you can take. And your strategy can even be different depending on which type of psi soldier you got. If not, it's not a huge deal, they won't make your play through significantly easier--just different.
Right now though, essentially for me they are strictly an end game class, good for the final couple missions. (Mainly because they effectively give me another squad member). But otherwise? As said above, I can't imagine wasting resources on them on a Legendary play through during the dicey months.
