2- I'd like to see recruits have differing potentials -- anyone could become a 'peasant' troop, many could become 'normal' troops, some could become 'skilled' troops, but few could become 'exceptional' troops. Training would bring out these inherent skill levels, not increase someone from one skill category up into the next -- ie no matter how much I train or what resources I have access to I'll never be a Michael Jordan or Muhammad Ali.
Combining these 2 ideas, I'd like to think that large armies of exceptional troops would not be possible, as they require exceptional people who, being exceptional, are in relatively short supply. No amount of training time, resources, technology, etc. could enable this.
But that forces you to field armies of troops of all sorts and quality.
First -- what's wrong with that? It adds choices which is good game design. Second, it doesn't force anything as you can freely choose to only use a certain unit(s). It may put you at some disadvantage to do so as you'd be deliberately restricting yourself, but tactics/strategies may even the field.
The best strategy would be to train all your exceptional recruits first, and work your way down the list...
Let's assume exceptional units take special buildings and/or special training and/or special resources and/or longer time. Will you go with no troops while you're recruiting/training your exceptionals, all the while defenseless (troopwise)? That would put you at great risk to an early 'rush'.
That's a little better than when the best strategy is just to mass produce your most powerful troops...
You wouldn't be able to mass produce exceptionals -- remember limits on troop numbers.
Let's say your population could support 1000 troops total, and 10% have exceptional potential. The choice wouldn't be 1000 exceptionals or 1000 normal troops, the best you could do is 900 normal troops (starting relatively soon) and 100 exceptionals (starting relatively slowly). This suggestion would prevent ending up with 1000 exceptionals (or any number > 100).
I don't think it's worth settling for that when it seems perfectly well within reach to have a combat system that allows all sorts of viable strategies when it comes to populating your army.
Differing skill potentials does not preclude/limit strategies for customizing armies, it does the opposite -- adds choices which is good game design.
Let's asusme there'll be some sort of rock/paper/scissors aspect (pikemen advantage vs cavalry, or firemage advantage vs cold), this would add another, similar, dimension -- large numbers of less-skilled vs. small numbers of skilled, multiplying options/choices.
It's also 'realistic' as not everyone has the same potential skills, and training can only bring one up to one's potential.