the way most users work their training is to focus on PG/SG or PF/C positions. they will rotate skills every few weeks (most commonly 2 weeks) since skills partially train other skills thus resulting in more skill increases. now with that said, users will take their trained players that have reached a certain level, usually at the point that they can no longer afford to train them or need money, and put them on the transfer list. once the player is sold they will have the money to acquire players that play positions that they do not train.
so if you have inside men that have prolific inside scoring, but mediocre-respectable ID, RB, and SB they will usually get passed over for players that have strong/prominent skills in all those areas. you would get more money with well-rounded players. so i would advise you to continue training C/PF and then sell some of them to get good players in the PG/SG/SF positions.