Deficient relative to what?

For example, if some other group G (perhaps children not of privilege not raised by educated parents in suburban homes) has stronger attachments, resulting in members of G having a lower chance of being converted, then we can say they are deficient relative to G. This theory is testable, at least in principle.

OTOH, if no such group G exists, but we want to alter our economic, social, and psychological evaluation such that children we evaluate as normal don't become cult converts, then this sounds more like a matter of how we define the word "normal" than any kind of statement about the world.