I liken DM training to boot camp. Boot camp prepares a person for becoming a soldier. It doesn't make them an excellent soldier, but rather gives them the tools to become one. Same with the DM course--it doesn't make you an excellent diver but instead gives you the tools to become one.
Whether a person decides to use those tools to become a better diver, or just sit on his C-card and brag about being a DM while wallowing in his own silt, is up to each diver.
Some people believe a diver should have excellent dive skills before becoming a DM. I don't share that viewpoint. As an instructor, I want to be able to mold them into responsible divers while the clay is still fresh, rather than break off any bad habits they've picked up during their quest to become 'better divers' before becoming DMs.
That's because good dive skills are just a part of being a good DM. DMs not only learn how to help other divers, but also become responsible for a large part of their well-being during a dive. That can be nerve-racking, even for experienced DMs and instructors. So if new DMs are focused on the safety of their charges and make that their top priority, I'm willing to overlook a few sloppy dive skills, which I can later work with them to improve.
Finally, whoever is the instructor that works with sloppy DMs shares some responsibility in them not having better skills. The instructor should be demanding better from the DMs, because their performance reflects on the instructor's. If the instructors aren't willing to help coach their DMs to improve their sloppy skills, that's a very broken group that I'd advise other divers to stay away from.