So if I understand these changes correctly, then there are now 2 groups of field players for training:
Group 1. Offensive players (AML/AMC/AMR/ST) who can be trained via friendly games.
Group 2. Defensive players (the rest) who cannot be effectively trained via friendlies, as it's difficult for them to become the MoM and get the 4%.

In that case, you wanna have your offensive players have as few white skills as possible (so only the role they play in), to make sure that the 4% get put on the most important skills for them.

Defensive players, on the other hand, cannot be trained via friendlies. They are much more bound to that 140% individual skill limit than the offensive players. Therefore, again if I understand correctly, you wanna have defensive players now have as many white skills as possible in order to train them efficiently, without their training speed slowing down?

The result would be as the following example: 2 players, an offensive and a defensive player. Both have a overall quality level of ~122%, their grey skills are 1% and their white skills are evenly trained. The offensive player has been trained with friendlies. That gives us:

an AMC with an average of ~ 230% on his 8 white skills
a DL / DC / ML with an average of ~140% on his 13 white skills

Is this what you wanna do nowadays?