We’ve had this debate quite a few times, I must admit even after reading all the messages in this thread my opinion hasn’t changed much:
Vietnamese’s weaknesses come from the fact that they have a weak-middling eco bonus and only weak military bonuses. Their “anti archer” identity is only realised very briefly at the very start of feudal (where the numbers are low enough that the hp bonus matters) and from early imp (when rattens start rolling out). In feudal & castle age they are realistically just a generic archer civ with nothing really going for them.
This is reflected in the stats that show that their biggest weakness is late feudal/early castle which is when they have their highest loss rate (well below average).
Personally I think we should either double down on their anti archer identity giving them a meaningful bonus for castle age (like free or discounted e-skirm) or give them some other form of power spike in castle age to help fend off Knight civs.
I don’t think they need huge changes though, just a few gentle nudges. (Having conscription apply at a reduced % in castle age is still my favourite).
Alternatively a rework of elephants to make them more viable in 1v1s would also acheive the same thing though I doubt this will ever happen at this point.
Edit: also please remove the gold cost on paper money