I imagine this to be quite problematic to model too.LOL. I have always thought the same. Specially in mods where you have to deal with colonial uprisings: Build a huge fleet of transports in less than 3 months -> Load all your troops -> Doom for anything that stands in your way. Like....to fight against 8 Rebel Militia Divisions with 20 tank divisions in Kaiserreich is a little bit too cheap.
Attrition through the roof caused by tunnel buildings that only the vietnamese and rebels can build? (generally talking about guerilla warfare here) Or unlocked by technology which vietnamese (and rebels) already start with, while other countries can only unlock by chance.