Well I dived for years without any formal training without incident. The relative lack of death is not proof that the training is good as I demonstrated by diving safely with no training at all.
IMO, NO instructor is going to be "good" until they come to terms with the weaknesses of the standards, stop assuming that the standards are "good" and learn to really teach diving.
Still, if you define "good" as compliance to standards then I'd say that most instructors are good. I just think the standards are beyond bad and into the "that sucks" part of the scale. LOL and agencies only toss out instructors who fail to follow standards. They don't toss them out for turning out lousy divers.