Wikipedia covers it pretty well:
https://en.wikipedia.org/wiki/Three-pha ... tric_power
But basically, yes because of the 120 degree phase shift in the case of equal current on each phase (and unity power factor loads, like a resistive heater) all the current actually flows between the phases and none of it flows through the neutral wire.
Whenever there is an imbalance either in amplitude or phase (such as a reactive load) the difference or imbalance current flows through the neutral. But this difference current can never be greater than the current of a single phase - hence the neutral wire doesn't need to be any bigger than the three individual phase wires, and in practice it can often be smaller (or even non-existent) depending on how well balanced the load is.
If the load is something like a 3 phase motor (which is inherently balanced) no neutral wire is needed at all.
In fact the motors in all modern EV's are 3 phase AC motors, either permanent magnet synchronous or induction, and they only use 3 phase wires and no neutral wire at all.