The height of your players may mess up training speed. 6'9 is just not that tall. Ideally a center would be 7ft+. You only want a shorter player when you want to train guard skills. PF train shooting and passing faster because usually they are shorter. Centers, though, don't need those skills as much. I would get a good price for your short "big" men and grab a tall trainee.
If you lose games, it helps to identify your weaknesses and where you need to purchase or train better skills. If you don't feel you are being competitive based on skill level, try more specialized training or buy some old players to address your specific concerns. Eventually if you do this enough, you should become just as good. If you are farther at the bottom of your league, spend as much money as you possibly can on scouting. It will really help you nab great trainees.
I feel very similarly, as I was just promoted and have a roster full of sub-standard players compared to the rest of the league. But, smart coaching and not necessarily having lots of cash is what this game is all about right?