Yes the whole "You get used to it" rationale is utter nonsense.
I was born and raised in Denmark, but lived in Texas for 20+ years and I never got used to the heat... in fact, I rarely ventured outside between May and mid-September. Now I live in western Washington state which is cool/temperate much like Denmark, and I feel "home" here.
South-East Asia just doesn't have my type of climate. I expect the only climate in Vietnam I might be able to tolerate would be Dalat, which I hear can be pretty nice since it's a mile high.
Dalat's weather is magnificent and I would love to live there. Unfortunately it is just too far away from stuff we need like immigration and therefore, the expat community that isn't married or have long-term visas tend to not be there. There is also Sapa in the extreme north of the country that is also elevated and actually gets snow a few months of the year. I've never been but I hear great things!
I'm glad to hear that there are people out there that have real-life experience with how you never really get used to it.