if you have average trainers and are playing 2 games per day, you will make 2-4 skill points per day. You play your first game, and get at least one skill point on average, then then train the reserves, then play the second game and get that second skill point and then train the reserves and players who still have condition for the next days games. I am sometimes amazed when, at the end of the day, I update my spreadsheet and see that a few of my players have gone up 5-7 points.
I figure in about 10-12 days I have enough skill points to give them a special ability and then work on quality.
Only this past season have I decided to give all my players a special ability. It helps that most of them are 18-20 and gain points fast. The tanking process allows me to do this and keep them 5* or better every non-tanking season. It also allows me to re-sell them easier as I keep them one point from the next star and they usually have special abilities. At level 20 it really helps when I can sell a player immediately.
So you dont have to power train if you can get the faster trainers, but it is frustrating to get that 5* player close to scout and he barely gets 1 sp per day. thats is when you dump them.