There is not the same (disproportionately small) percentage of people with potential for good middos and ability to intervene successfully as there are superstar ballplayers.
I think there has been some confusion here because avhaben (perhaps mistakenly) shifted the focus of the conversation.
Originally, we were talking about rabbanim who are capable of giving effective marriage therapy. There, I grant you that you don’t need to be a statistical outlier to be successful.*
However, when you start talking about “the next Rav Pam” and “the next Gadol HaDor,” (as avhaben began doing) then you are dealing with outliers, and there my argument stands.
My apologies, as I went along with the shift of focus without realizing it as well.
The Wolf
* Even so, my point about dilution of talent applies here as well. By adding more students, you’re only going to produce (on average) lesser talents, not greater. Those with the temperment, desire and ability to be rabbinical marriage therapists are already training to do so.