I had a level 6 trainer for most of the time the staff system has been set up like this. I went down to 4 a couple seasons ago because the offsite forum stuff showed it wasn't much slower. I haven't tracked progress too closely, but the difference hasn't been huge. The really don't like the staff system in this game at all. I think you're right though about how long you can train a player with higher levels. I mostly trained younger guys though, and I think it'd be a fair bet to say I'd have at least 7 or 8 million more in my account if I could reverse time and have used a 4 all those seasons.