Of course none of that is wrong... When I learned, however, from amplifier designers that the design of the speaker cabinet has an effect on the behaviour of the output stage of the amplifier I started to realise that music amplification was an awful lot more complicated than I thought. The question boils down to whether the vibration patterns of the body have an audible effect on the vibrations of the strings, and how great that is.
The apparent existence of the phenomenon of bass guitar neck dead spots, for example, suggests there is some audible effect in some circumstances, but I haven't come across anything to actually put numbers on.
Maybe I should make an instrument with interchangeable bodies and try doing some tests.