Let me address a couple of issues within this thread. First let me point out to those of you who do not know me that I have been an instructor for over 10 years and currently provide appraisal education in the state of Florida under the name Institute of Real Estate Studies, I am also a general certified appraiser.
I see trainees all the time in CE, ABII, and ABIIB classes and I see no difference between relatively inexperienced ones and the "I've been an appraiser for six years" crowd (to which my responce is always, you are an appraiser when you can sign one all by yourself, right now you are a trainee). Passing the state exam is, and should be, the bar to demonstrate you no longer need supervision, not how long since you passed a pitifully easy ABI class and sent a check to the state.
Concerning the business model side of it. Yes, bringing in trainees may be raising your competition, but that was the model for decades in the real estate brokerage business. Now, the broker recoginzes they cannot just milk the salesperson. They must give the person a reason to stay with the firm. This is why RE/Max is around. The firm provides certain services, but the individual reaps the major part of their efforts.
Trainees need direct involvement with their supervisor, and on a constant basis. Four trainees is being generous. If each does 10 appraisals a week, and gets 20 minutes of supervision per job, that is over thirteen hours of "supervision" per week. Problem is most supervisors get out the red pen circle the "problems" and sent it back to the trainee. Hardly an education/training process. Also, I hear of trainees going into areas their supervisor has not worked in recently, or has never appraised in that area. Thereby calling in to question the supervisors geographic competancy. Wanna bet, only a handful of supervisors say to the trainee "Lets go out and do that one together"
Also, you should see their eyes light up when they do the case study in my ABII class. They laugh about the fact the adjustment is what you need, or what your boss tells you, and then they find out that adjustments shouldn't be, nor need to be, POA'd (pull out of air - polite version).
Think about law firms, doctors, engineers, accountants, etc... They could all open up their own firms but they realize that small groups often yield more than the sum of the parts. For a bunch of people that analysis things all day, we are woefully blind to our own business cycle.