I understand the viewpoint of cities not being the right place everypony to live comfortably, before judging all big cities consider the following:
-Cities are where people of different ethnic backgrounds need to cohabitate ie taking the subway together, share common spaces like shops and restaurants, and living on the same block if we're taking about major US cities.
-It is harder to get oneself noticed in the city when starting a career because there are more people doing the same thing and competing for the same jobs. Notice the try-outs Rarity was working so hard for.
-Cities on average are more expensive than neighboring towns.
With these examples alone it is apparent that living in a city can be harder to live in than a small town. "Rarity Takes Manehattan" was most accurate when the episode was driving the point that ponies who live in dense cities don't have the same laid-back attitude as the ponies in Ponyville. It's harder to make friends because survival in the city is everypony's main concern, eventually everypony adapts a hardened attitude. Ultimately lesson I learned and that I want everyone to take away is that even when everypony hustles day and night in the big city it is still important to show a little bit of kindness toward others. Here in the big city is where we need it most.