It certainly would lessen the pool of graduate students at ALL if they stuck to your guidelines. While I know I would benefit vocally from just working and paying for lessons, but if you want training in opera you must be involved in a program. You also can't create the same learning environment when you are isolated on your own versus a real Community of Learners. And, despite your professional experience, you need that Masters degree to be eligible to teach later on. I've been on both sides of the fence.
That's my polite way of saying it's a completely unrealistic rule of thumb, esp for female singers.
