Your examples above perfectly illustrate the problem.
The Vietnamese, Khmer, Malay, Thai, and others in the SE Asian region are not of the same ethnicity.
So if one wants to conduct political opinion polls based on the East or Southeast Asia geographical region, that's one thing.
If one then says "Well, it's really a poll of the Asian ethnicity," it is absolutely stupid.
There is no "Asian ethnicity."
Your absolutely right.
However, that’s how researchers-demographers categorize and label.
Researching ‘Asian’ as a demographic yields some very interesting contrasts among ethnicities if you can find studies that break them out.
If my memory is correct, the Indian population had they highest family stability scores and fit the model of what we once knew as the traditional family (highest rate of marriage, lowest divorce rate, child abandonment does not exist, strongest cohesiveness of extended family unity, and virtually no one lives alone - always with a bro, sis, cousin, aunt or some familial relation.)
They also had the highest rate of Bachelor, Masters and PhD degrees, surpassing the degree holders among White-Americans. They also had <.01% figures on incarceration as did most of the rest of the labeled ‘Asian ethnicities.’ But, at the same time, we need to examine this from the perspecitve that only the most fortunate of the native India population is able to immigrate to the US.
If I find a link to these studies in the next few days, I’ll ping you back here.