If that was the case, the KnA would conquer California and Russian North America.History doesn't really have a protagonist - I think that's the model AHB is following.
Their population is too low to sustain against the US, and all the Russian immigration to America is unjustified in the first place. The Russians are not that stupid. They don't even have the Baltic Ports, sending colonists to a place they can't properly defend doesn't make sense.
Russia can't send a single grenadier to defend Russian North America against American aggression.