I am not saying $5k, I am saying $35k. With that amount of money, you can certainly afford to live a super comfy life in Thailand not in a shack AND afford an iPhone.
I agree with your premise in general though, because given a similar lifestyle and similar percentage of savings (let's say 10%) from your salary you get in a high COL place vs. low COL place, high COL place would be more preferable, as that 10% will be higher in absolute dollar value, and a lot of goods are priced the same everywhere.
People seem to actually believe that 5 thousand a year gives you a middle class lifestyle in the third world. The cost of eating only rice and beans and living in a tin shack with dirt floors is pretty much the same everywhere.