HDI comparison of Cambodia, Vietnam, and Bangladesh [0]. Notice how Cambodia and Bangladesh used to be developmental peers until 2010.
Life expectancy comparison of Cambodia, Vietnam, and Bangladesh [1].
Mean years of schooling in Cambodia, Vietnam, and Bangladesh [2]
Gross GNI per Capita PPP (log normalized) in Cambodia, Vietnam, and Bangladesh [3] - the only metric Cambodia is roughly comparable to either country.
There is no way around it - the average Bangladeshi let alone the average Vietnamese is healthier, better educated, and richer than the average Cambodian. And this divergence only began in the 2010s when Hun Sen and Cambodia's political leadership began backsliding into kleptocratic authoritarianism.
[0] - https://globaldatalab.org/shdi/table/shdi/BGD+KHM+VNM/?level...
[1] - https://globaldatalab.org/shdi/table/lifexp/BGD+KHM+VNM/?lev...
[2] - https://globaldatalab.org/shdi/table/msch/BGD+KHM+VNM/?level...
[3] - https://globaldatalab.org/shdi/table/lgnic/BGD+KHM+VNM/?leve...