I was talking about indicators used in grouping countries as LDCs while you have decided to talk about something totally different which is per capita income of a country. Everything you've said about per capita income is 100% true only that you failed to realize that per capita income is just one of the indicators used by UN to group countries as it falls under socioeconomic development.
I'll give you a very simple homework. Do some research on LDCs and tell me where it's indicated that per capita income is the only indicator used in grouping countries as LDCs or not. Per capita income is used just to compare wealth of a nation against others. It is not used to determine how developed that country is. You can be wealthy but not developed, get the difference.
A country is considered an LDC if it meets three criteria which are poverty (and this is where per capita income falls), Human resource weaknesses which include things like literacy levels, health, education, nutrition and many others, and lastly economic vulnerability.
Do some research and broaden your knowledge