I really dont know what point you are trying to make with your posts. Fact is, that we have hundreds of thousands players in this game that are junk data, part of those are rookies that get dumped right away because training them makes no sense.
i want to point out, that your initial statement makes no sense.
Now you can argue that a 15k player is a beast in a low league, but does it hurt if there is still some room left to improve him? Why would I train sixth man potential players if I can pick up Allstars from the market for a handful of money anyway?
If the potential don't offer boundarys we could go back to the pre potential days. Since with this logic you can screw every lower limit, and you will do it, since the low potential players are unintressant for a lot teams, since there are so many better ones out there. The quality of training who get used, depends of the existing material. If you like to have every trainee usefull, they all had look the same ;) but the amount of trash wouldn't change then.