here's something to think about... how did you get through YOUR training? do you think your sensei/sempai had the same feelings about you?
time to give back a little.
Why doesn't the dojo have more yudansha? Perhaps it is something in how the dojo is operated and how the classes are taught, that make them disappear. Maybe they all get worn out by having this burden laid on them. They don't yet know how to learn from training with beginners, and they seldom feel they get much out from practise.
Teaching mixed level classes, including beginners, while giving something to all levels is difficult.
I really don't think that those who never trained in such a setting, and much less taught such classes, will understand.
Perhaps you recieved lots of pushing and help before the shodan test, and now your teacher puts part of that energy elsewhere? Still, it's not clever letting the advanced students feel they are almost forgotten and ignored. David S, maybe you should talk to your teacher about it. There's no guarantee you'll have satisfying answers from him. But maybe you'll get him thinking. Perhaps he can compensate you by tossing you aroung for a couple of minutes, a couple of times during class, so you'll be happy to go back to the beginners to get some rest
or something like that. (Oh yes, you learn a lot from taking ukemi from skilled people) OTOH he may get angry at you and think you are ungrateful. Well... you are already thinking about leaving if the situation doesn't get any better, right?