Thanks for the reply Otterman. I suppose I have been in what I call the "traditional" pattern so long I forget people may have joined in the "Seat and Seniority" system.
"Traditional" to me is when pilot pay depends upon your position, your seniority and the aircraft type you fly. To me "Seat and Seniority" is when your pay only depends upon your position and your seniority. For example, a 15 year captain on a 737 has the same base pay as a 15 year captain on a 767. It looks as though your charter operation is what I would call "Seat and Seniority".
At our company we get massive swings in training volumes every time we change business plans, costs are massive. Also, as with your company no doubt, pilots must change aircraft to make higher pay. I cannot help thinking there must be some trade off between the company saving training costs and the pilots getting an easier life which would make "Seat and Seniority" beneficial to both.