Really, saying that a type sucks relative to other types is just plain silly. It's not like every Pokemon of one type is going to have the same base stats, movepool, or abilities, so it's pretty unfair to judge a type via generalization. This especially applies to a type as diverse as Psychic. The Psychic type has plenty of Pokemon to assume many different roles, be it specially based (Alakazam, Lati@s, Espeon, etc.), physically based (Metagross, Medicham, Gallade, etc.), support (Gardevoir, Cresselia, Claydol, etc.), or even a mixture of any one of these roles. So to say that Psychic is "worse" than any other type just seems foolish.
That being said, I will concede that a Mono-Psychic typing is just suffering, and it has been since Generation 2. And unfortunately, many stellar Pokemon are faced with this, including Alakazam, Espeon, and the Deoxys Forms. The only type Psychic resists is Fighting (and itself, duh), which isn't anything special considering literally every Fighting type carries something to hit Psychic- types with. And with Knock Off being extremely common this generation, it only adds to the issue. Psychic's three weaknesses are also common offensive types, especially with Aegislash compounding the issue.