You're comparing the past with the future. I am not proposing one giant managed thing like an airport but much like a small town where you can rent store space and open up any business you want. Although, even it would be for most basic needs. You would still be able to travel to other cities and megabuildings easily because transportation via rail and other means would be much cheaper and convenient. If this was central coast cali for example, you can have one hour rail to LA,San Francisco, and perhaps close enough to most state and national parks and beaches. I do not support people never living the megabuildings but to your point my local fastfood, walmart or even chinese,indian,mexican,etc... foods unless I venture out a bit are mediocre as is the case in most smaller towns.
The thing is, there cannot and should not be another new york or manhattan. We need future cities to be energy efficient, sustainable and defensible. A city that would last the next two or three centuries allowing our current culture and history to be passed on is important and I am not sure cities like new york will be pleasant to live in by the end of the century nor are they or will they be cheap. That said, there many millions of people and they can still continue to live in existing cities but we can't just keep building more LAs and NYCs or continue to pretend homelessness, high rent/house prices, the ridiculous infrastructure required to support cars and the ever depletion of agriculture friendly land and sustainable water are not a problem. Now is the time to fix them not when famine and disasters are killing millions.
But to counter your point about mediocrity, vegas is a good example. I have terrific food and entertainment there despite the seemingly endless interconnected structures of hotels and casinos. Perhaps given the proper financial incentive things can be not so mediocre?