How can one guy make them stronger?
Isn’t he already part of the organization, even if just as a higher-ranking associate?
So him getting made wouldn’t make more people joining in. If he’s as respected as you claim people might already follow him. Made or not.
He has much more power if he becomes made, because then that will set him up to become a Capo and then a boss. Therefore that makes the Outift much more powerful with him having more control of his crew that he is assigned to and eventually the entire organization. He's young and has a promising future so get him made if they care about the future of the Outfit. Its a no brainer.
