I actually prefer the RTW I system (at least in EB) greatly to the RTW II when it comes to replenishment and recruitment in general.

In EB, let's say I invade Gaul as Rome. If I want to replenish my armies without using mercenaries and merging existing units, reinforcements need to march over or around the Alps and join up with my forces. This offered a lot of strategy to the game. The AI often (likely by chance instead of a grand scheme) would cut off incoming reinforcements, and armies deep in enemy territory would literally be trapped. Overtime, their composition would become closer and closer to that of my enemy, as mercenaries were increasingly used from the region I was invading.