For example.
Veteran has strong inside defense and strong experience.
Rookie has atrocious inside defense.
Rookie trains at a rate of 1.2
The formula I am suggesting for determining this is
(average of xp+ lvl of skill)/4
So, strong xp and a strong skill comes out to:
(8+8)/2
(8)/4
2
Divide 2 by 10 then add it to the rate at which the rookie trains. (2/10)+1
So while having strong and strong issues a boost of .2, the highest xp level I have seen (14) combined with a skill of 14 provides a .35 training boost. If somehow someone managed to get a 20 and 20, it would only increase training by .5
I think the math is pretty simple, and the fact that the rate of training is not doubled, the Max it could possibly increase is .5 provides a reasonable training boost without unbalancing the training system.
I am merely sharing possible ideas, if this wouldn't work let me know.