But cities designed around trains are superior and it was a contemporary technology that was ignored.

No, they were not. Trains are good for taking large numbers of people from one place where they don't want to be to another place where they don't want to be. In certain situations that can be a useful thing to do, but you can't design a city around it.

And yet we created trains that are a more efficient way of traversing cities built around horses as well.

Why can't you design a city around it? It would be different than Houston or LA, but would that be a bad thing?

> They definitely smell bad

??? No, they don't. They only smell bad when they're kept standing in their urine, which is still not worse than a hairdresser. Compared to dogs (or ICE cars) horses smell way less. They do sweat to regulate temperature, which has a distinct smell, but it's way less irritating to a human's nose than the sweat of the rider.

There's a set of distinct smells associated with the horses, but other than the piss, none of them are particularly "bad". In my experience, humans tend to smell way worse overall (from food to body odor to the excrement) than horses.

Cars replaced streetcars, not horses. Few people in big cities were getting on horseback to commute to work in the morning in the early 20th century. People generally walked or took the streetcar.