While Psychic isn't the WORST typing Defensively (that honor goes to Ice), it's still not something anything defensive wants to have in this Meta full of Aegislashes, Bisharps, and Knock Offs. Look at Cresselia; it has 120/120/130 defenses and a decent support movepool with gems such as Trick Room, Thunder Wave, and the exclusive Lunar Dance. It still sucks because of the aforementioned threats and lack of resists outside of Fighting, which isn't as common as last Gen (the only relevant OU Fighting-Types are Conkeldurr, Keldeo, and Terrakion). If Cresselia was ANYTHING else it'd probably be UU or OU right now. Hell, even if it was an Ice-Type it might actually rise in usage.
252+ Atk Dread Plate Bisharp Knock Off (97.5 BP) vs. 252 HP / 252+ Def Cresselia: 260-308 (58.5 - 69.3%) -- guaranteed 2HKO after Leftovers recovery
252+ Atk Dread Plate Bisharp Knock Off (97.5 BP) vs. 252 HP / 252+ Def Cresselia (Ice-Type): 130-154 (29.2 - 34.6%) -- 100% chance to 4HKO after Leftovers recovery
The only real perk of being Psychic is STAB on Psyshock, which isn't too much of a consolation nowadays thanks to Chansey being used over Blissey most of time (but lets you win Calm Mind wars, at least).