I agree with your assessment. But I do believe Sai Gon ( HCMC) will surpass BKK in a decade with all the things you stated that makes BKK such an amazing city. Sai Gon is transforming at a break neck pace with a modern and high tech airport coming soon, the newly open sky train is planning to expand the entire city, and infrastructure will only get better.
Lastly, both major cities in VN are attracting tourists, mostly the quality kind, without the allure of an established sex industry.