If universal healthcare was a good thing then people in Rwanda should be more healthy than in the US. They aren't, so universal healthcare is bad.
Find the flaw in this argument and you'll find the one in yours.
84/100 mega-cites are in the third world.
I don't know how this could confuse you but feel free to google inductive reasoning.
http://www.prb.org/Publications/Datasheets/2013/2013-world-p...
As for the one I gave a negative opinion about, a big part of my dislike for Delhi is due to the lack of density - it's more suburb than city. Going from where I work/live (Pitampura) to the fun parts of town (South Delhi) takes 1-1.5 hours and the metro shuts off at ~11pm. (Other things I dislike are pollution, oily food, and the difficulty in finding a date.)
India almost certainly will be better off after people escape rural poverty and enter the middle class living in the cities. This process is happening rapidly and the results are good.
Indeed if mega-cities were a good thing then Pakistan, Nigeria and the Congo should be doing better than Japan. Excepting just 6 out of 84, your list thoroughly proves my point; over crowding correlates with societies with suppressed labor value.
And by the way, in spite of adding endless supply of housing, none of these cities have cheaper real-estate than the rest of their country.