yes, it's true, even a slightly-optimized vanilla cipher will easily out-generate focus than a psion.
however, an optimized vanilla cipher/caster multiclass will never be able to out-generate the focus gen of a psion/caster multiclass.
an early psion build i did was a psion/lifegiver. that thing carried my party for similar reasons to boeroer's post. if my party needed buffs or healing, i excelled at that and did that. by the time i was done casting spells i had tons of focus for cipher powers. i would basically switch between being a psion or a support caster and i basically always had uptime with spell casting.
whereas a normal, un-cheesed cipher *has* to spend time physically attacking to generate focus, a psion/caster multiclass essentially generates focus by casting spells from the other caster.
also i think you're underestimating the power of being able to endlessly spam powers. it is true that objectively speaking a normal cipher can out-generate a psion, no normal cipher can indefinitely paralyze-lock an enemy - at some point they have to stop and attack for a while. a high level psion can in fact indefinitely do so, and in fact i set up some AI scripts at a certain point that would either spam burst or mental binding and it is shocking in how many fights you can get away with doing this and trivialize them.
that being said, a SC psion is not nearly as powerful as a MC psion IMO. if you really want to get to tier 9 powers you can, but you only get slightly more focus generation while still having a lot of drawbacks. a caster multiclass pretty much covers the main drawback of a psion, which is well worth losing tier 8 or 9 cipher powers.
edit to add: historically there was a lot of skepticism about psion when it was first released in patch 4.0. and the thing is, there's a lot to be skeptical about, if you imagine playing a psion is just like playing a normal cipher. but in truth, a psion ends up playing very differently than a normal cipher, and is very powerful at that alternate playstyle. for me it was really a "see it to believe it" kind of mental switch i had to do.