So what you're saying is the mount won't make the iphone's antenna any better at all because both can't be used at the same time....BUT, when using the mount it will be much more reliable in comparison to just using the naked iphone??
Correct. The GPS antenna in the iPhone is tiny. If you look at the teardown photos online you can see that the cell and gps antennas are compressed into one little antenna plane which is much smaller than your typical GPS patch antenna. Using their dock, TomTom is choosing to hand off the reception to their own antenna which is always optimally positioned toward the sky, not a dashboard or a seat. Using more than one antenna could result in multipath reception from two different sources and digital processing doesn't handle that very well.
I'm not sure exactly what you're asking here because all you did was restate what I already stated in the text of mine you quoted.