Thank for your response. Your last two sentences had special meaning for me in understanding the concept of developmental arrests.
"Inevitably these will be disappointed and the resulting disruptions in the therapeutic relationship become either failed therapy, or, if managed competently, can become instances of repair of the relationship and therefore moments of renewed growth of the self and of healing. But, please note, it is not the satisfaction of an adult's infantile needs that is therapeutic but the repair of disrupted relationships with the therapist. "
It has seemed to me that in the end, the beloved parent must fail the child's infantile needs. But a continued warm relationship repairs this failure. And it seems this is recapitulated in therapy.