Answer :
per capita income tells us about the income of people but does not tell about the income earned by an individual.Yes, per capita income is vague. It don't tell us about health condition, education condition, etc of a country which is very important to measure development and prosperity of any country....
I think yes per capita income is a good way so that we can see if a country is developed or in developing stage,Because from this we can see the income of population.Although there are some defects like the income of all people is not clearly defined ie the per capita income of a country will be high if there are more rich people then the poor people.