I don't think the root cause(es) of psychosis have really been determined yet. I think it's fair to say that since many drugs induce immediate psychosis, it's unlikely that pruned connections are the only cause.
It’s pretty clearly D2-like receptors being overexcited, at least as far as cause and effect. Hence psychotic symptoms in stimulant users and a remission of psychosis in schizophrenic patients when on D2-blocking drugs.
Psychosis resulting from meth withdrawal has always suggested to me that it is an under-connected problem because presumably what happens during withdrawal is widespread "disconnection" resulting from a large decrease in synaptic sensitivity (caused by a flood of neurotransmitter, meth) and a steep drop in neurotransmitter activity once the meth is gone.