"Vietnamese music is shit" - if you are talking about the garbage coming out of Communist Vietnam then yes.
However, anyone with the least bit of musical refinement will see that the Vietnamese love ballads from the Tien Chien era have both excellent musical qualities and meaningful lyrics - a rare combination in Asian, and in Western, music in general.
See anything by Doan Chuan - Tu Linh. Old school, yes. Shit, no.