I've seen a number of problems that come with self improvement and behavioral changes through faith:
~ Let go and let God; very often God doesn't come through, and that can feel like a betrayal and become a relapse.
~ Religious faith often comes with ideological baggage. Mainline and fundamentalist Christianity, for instance, have ingrained prejudice against women and LGBT+ folk, and depending on the faith, persons of color.
~ Institutions that engage in faith-based group support such as 12-step programs are covers for labor exploitation cults, and those who have benefited from those programs are then pressured to provide free labor to their program elders. That's exploitation and abuse.
Now, I don't have figures from trustworthy sources regarding the positive-outcome rate of faith based recovery programs. I don't know if longitudinal studies exist that are not by sources with an agenda, so I'm relying on personal experience, which is therefore anecdotal. But from what I've seen, depending on faith as the foundation of your recovery is risky.
This isn't to say 12S programs are worthless. In fact they use a shotgun approach and offer several pillars of support, many of which do not depend on the second step. But 12S programs are run with an ulterior motive, so it has a similar risk as sending a troubled teen to seek counsel in a youth ministry. Buyer beware.