While there’s going to be a lot of growth a lot of the same things can be said about Vietnam. Foreigners will never win an argument against locals, some locals will die on a hill defending the 150-200 AQI for 5 months out of the year. I don’t mean this as advice to avoid Vietnam, but just that 1/2 the bad things said about China apply to most Asian countries.
I think Vietnam probably captures the atmosphere of China 20 years ago. Plus, Vietnamese people tend to be much friendlier and have better English literacy. I lived in Beijing and Shanghai during the good pre-Xi times, and I'm dying to go live in VN for a while.
In many major Chinese cities you literally cannot see the sun bc of air pollution. No major city in VN is this bad. Will it get worse? Maybe but I wouldn't necessarily expect it. VN people actually do get quite concerned about the quality of their food and, if air pollution started to become a visible problem, in places like HCMC, I doubt people (govt officials included) would be OK with that. The drive for money is hard but not quite as no-holds-barred as PRC.