As a rash young engineer at JBL I made that statement about the old 075 tweeter. They had a very distnictive (generally bad) sound and I stated that it was inherent in the aluminum diaphragm, that even if they could be made to measure better the sound character would remain.
"Most things really do sound like whatever it is they're made of"
I guess I'm not alone in this opinion.
Sombody called my bluff and I had to set up a comparison between two 3-way systems, identical except one had the 075 tweeter grafted on. We used a new 1/3rd Octave equalizer to try and get the response of the ring radiator to match the smoother performing 1" dome.
The response of the typical 075 was primarily composed of 3 individual peaks. That was the good ones that the lady had creased correctly with the tip of her ball point pen (honestly!). Still, with an equalizer I could get the response to be a pretty good match to the 1" dome. Surprisingly, as the response got closer to that of the dome, the sound became the same as well. The "aluminum" character disappeared.
Material, of coarse, determines the response of a driver, but if you can fix the response that material related character will disappear.