if the neutral is sound it will suck up all the return path much better than any water pipe
If the neutral is sound it will likely carry more current than any other available path, but all available paths will carry some current. Even a ground rod in the dirt will carry some but it likely will be such a low amount it will not be easily measured.
How much current flows on any one path depends on the resistance of that path. Put some current on the service neutral and it will develop a voltage drop across that conductor, that is the nature of conductors. If you could create an ideal conductor that has no resistance even when carrying a load then you possibly can have all the current travel that path and no other.
Most of the time the resistance of the water pipe is just as good, maybe even better as the service neutral and they can both easily carry about the same current.
Neutral current is not trying to get to ground, it is not trying to get back to the neutral conductor at the service, it is trying to get back to the XO terminal of the transformer it is derived from. It will take the easiest way there. The easiest way does not have to be a single path, and often is not.