There are tomes written on this subject, but I'm going to keep it as brief as possible.
What makes an effective defense? What makes an effective offensive? What results in a unit surviving or dying? Armor, constitution, skill, weaponry, support from other troops. Skill, IMO, results from innate ability + training + experience. There is no substitute for experience in RL and there shouldn't be in game either. Armor, training, etc., these can vary as is appropriate, but experience is a result of real (not simulated, practiced or theoretical) combat experience.
But as far as varying the amount of training, I don't think that this is a variable that will serve the FPM mod well and I don't think it will serve any mod in GAE well unless we wanted to support an actual fine-grained experience point system. This would be the only way that I can see to effectively support adding the variable of training and I don't think I'm personally interested in that at this time, although it is possible to implement such a system while not breaking the base tech tree or any existing mods by assigning static values to NOS (not otherwise specified) kills (e.g., 1 kill = 100 xp). Right now, we have MANY moving parts that are not yet attached and I strongly feel that we need to put these together before looking for more moving parts to add to the mix. Just my opinion.