Which is one of the most common thing in the current meta
No, it’s not. Vietnamese arbalester tank 8 shots, Italians would tank 10. This means that the italians arbalesters would be really good in imp in one of the most common situation, the arbs vs arbs fight
Now, let’s analyze a couple of other options.
In feudal and castle it is just a straight up better version than the Korean, because it is still free and on top of that you can get your usual armor upgrade for a +2 defense in feudal. Archers have 30 hp and in an archer vs archer fight with full upgrades they would take 3 hits instead of 4. This means 10 hits instead of 8. if we compare it to viet archers (FU), they take 9 hits.
Now, let’s talk castle age (not considering pavise): italians crossbows could tank 9 hits instead of 7. Now, here vietnamese can tank 9 hits from other crossbows, just like italians, but the latter on top of that, also have bonus on the university with cheaper balistics. If we count pavise (and we should not, since it requires a castle), italians crossbows get up to 4 pierce armor, which means that they tank 12 shots.
Those bonuses also influence the fights when skirmisher are mixed, wether you think it matters or not, and cav archers. Pierce armor is an incredibly strong stat in aoe2
So, it is a bonus that influence the early game (since you are facing someone having straight up way better archers than you), probably forcing the opponent at either outmassing you or going for skirms. Going for skirms or outmassing you means you are later to castle age (which usually you are going to be anyway since they need less res to click up) and that would lead to a really strong castle age transition with the immediate balistics.
The problem is, that this also buff them on arena/closed maps (a settings in which they are pretty good) by making their arbs just straight up better (and it kinda matters when you are rushing imp to get the arbs power spike) and on hybrid maps (again a setting in which they are already good) by giving them better options.
You people continue to repeat that what they need is a buff to their military to make them more competitive on open maps, but forget that a military bonus makes them better in basically every other setting except water.
Not every civ has to be equally viable on each setting and on top of that they are not by a wide margin the worse civ for open maps