I think, when someone doesn't know a whole lot and doesn't have a lot of skills, plugging into a well-oiled system can be very useful for rapid development. (As a friend of mine says, GUE Fundamentals can make a 30 dive diver LOOK like a 100 dive diver, but they still AREN'T a 100 dive diver . . . ) When you gain extensive experience and skill, and especially if you begin to push limits on what you do, you can look around and judge what you're doing and whether it's working for the direction you've ended up going.
When I started diving the whole GUE system, I was enthralled because it seemed to work so much better than what I had been doing before -- and I still feel that way. Eventually, I figured out that some of the things I liked were virtually universal in the cave diving world -- the buoyancy control, the trim, the non-silting propulsion, the lights used for communication, and to some degree the team operation. I also learned that there were beautiful, careful, safe divers who used other systems and protocols, and I love diving with some of those people. To date, I have not found, nor do I at present contemplate any diving where the system I'm using would be an impediment, but I recognize that very deep dives, and penetration into very small cave, are not great places for the choices that GUE has made. (Never mind that they DO very deep dives, and do them safely; one can easily argue whether the way they do them is the best risk-benefit strategy for such dives, and I won't make those arguments.)
At any rate, I wish the general recreational world learned better buoyancy, better trim, non-silting kicks, better situational awareness, and better buddy skills. The DIR system incorporates those things, which is why I think that kind of training is most useful for people who never intend to step outside the recreational range of diving.