There are a number of levels once can enjoy a film including just pure spectacle, intriguing story or understanding the sub-text. I didn't really get the last one until Back Panther and now again with Da 5 Bloods. Indeed, the comments on Da 5 Bloods remind me a little of the comments around Black Panther.
I won't pretend that I understand what it is like to be a war veteran, but as shown in many films, it can a complicated mess. Add on top of the complications of fighting for a country you know hates you for no reason. The enemy knows this too and uses it as a propaganda tool you have to deal with along with the other psychological issues only a war veteran who has been in battle will truly understand.
Thinking about most of what I just said, is that really sub-text? It seemed pretty clear to me. But maybe the experience of the Vietnam war told from a completely different viewpoint along with some deliberately amateurish camera techniques could be alienating for some.