Any psi spamming pyro is doing a very poor job. Even on boss fights there's so much more potential.
For example a boss might be immune to control/stuns but the monsters it summons (the real threat to your party) are not. Using tele pull & mental pulse, a skilled psi will be able to knockdown/stun/slow all of these enemies whilst your party deals with them. Quite often this is the difference between success & failure for a group.
For straight up dps fights you can use certain combinations of skills & rubies to give you an almost constant 100-200 boost to intelligence. Pyro might be your main attack but there's no reason why it should be your only one.
My advice is always to pick a class you enjoy playing & form your style around what works well for you- don't worry about what these 'endgame' players are saying, because chances are they aren't very good.
How have you found the psi so far? What level are you & what skills do you use most?