Cats deter rats passively but cats don't regularly hunt adult rats.

Cat colonies would not survive in subways because the food sources are better in other safer places.

Also crazy cat ladies do not dump cats around homes. Bad owners dump cats around homes and crazy cat people come fix the problem for you.

The real truth is cats and rats are attracted to some of the same food sources, trash. Rats have lots of other options as well, which is how cats can carve or a territory from rats, but nothing will make a real difference until the city fixes the trash.

Rich neighborhoods dont have feral cat colonies because they pay more to handle their trash.