Ive seen very experienced airline pilots who made lousy instructors, the most important quality an instructor can have is the vocation to teach, the licence/ rating and knowldge is secondary to the attitude.
A good CFI manages his instructors and brings them on especially new ones. The main problem with schools and clubs is the lack of this professional management .
I remember a peculiar chap at Birmingham who spent ages studying for professional licences etc and eventually took over all the flying schools at Bham. He managed to blag his way through an IR and a CPL and an QFI rating but the one he never managed to get was a FIC rating -why because he just wasnt good enough.