Well, AOR alone puts a big strain on logistics, sending back armies to retrain can be a serious pain...
I once devised a system where you could have all units available from the start but with extreme recruiting time.
Barracks and smiths wouldn't give bonuses but rather reduce training time and cost.

While it worked in reducing somewhat number of battles and limiting elites it also gave the player an unfair advantage since retrainig takes always the same time and AI doesn't do it...