Code:
"DelayBetweenPokemonCatch": 1,
DelayBetweenPokemonCatch (Value)
Delay in milliseconds between attempts to catch a Pokemon.
While what you're saying is correct, keep in mind there's also a Walking Speed. if you were to set it to 2000km/hr, then yes you'd probably be catching pokemon every millisecond ;P.
Right now on the 100km/hr walking speed, it's able to catch a pokemon every 4-6 seconds.
Currently I don't think Niantic has a detection system in place so they have no way of knowing what your catchrate is. All their softbans are based on distance to time travelled.