The other thing is that, at the end, we're talking maybe the difference of a couple of weeks of training over the course of many seasons. If you're looking to completely maximize a player's ability, of course, going to that level of detail may be necessary, but if you're building to a specific target or even just a general profile, it might just be best to go ahead and train the player to get to the skills you need in a manner that makes him most helpful (i.e., instead of trying to min/max elastic effect, maybe train him in an out of position skill in a week where you have easy or unwinnable league games, and in his most natural position if that week it may mean the difference between a win and a loss).
I can't agree more, though, with you and Lemon that you don't want to end up not being able to reach the levels you want in the skills you find important because you were too focused on 'efficiency' and the skills you got to speed up his training ate a bit too much potential. That shouldn't be an issue for a well-managed, intelligent training plan, but for dopes like me who trained three seasons of JR, then a ton of SB, and are now bumping into cap range trying to get some OD, it may present an issue. (Of course, in my case it's just the slowness of training at their age now, not cap issues yet, but I've already had to scale my target OD down even if speed weren't an issue).