You really think so? I'm basing everything I say off of personal experience.
I've tried hundreds of different speakers over the years and each one has had its own special character.
Wether or not it was some type of distortion , resonance in the material in its usable range , damping or whatever.
Tuning is awesome and very powerful I agree, but, even among good speakers but to say that different materials don't have differing sonic characteristics seems absurd.
I've used bottom of the barrel speakers on up to stuff that some people would only ever dream about and there is always a difference.
The entire journey has been me asking one question after another. When a speaker behaves a certian way I always want to know why. I used to truly believe that I could buy cheaper speakers and make tune them into what I wanted them to be. I've gotten quite good over the years at doing just that to a degree.
I'll give an example.
Until recently I ran a set of the focal flax. Pretty good speakers and I spent almost a year tuning them to get the absolute most from them. I spent a month on tweeter placemat alone.

I recently purchase the utopias.
I dropped them in, same tune, laid each tweeter face up on the dash , mids in the same locations in the door and given they required very similar power didn't touch my amps.
The sound was instantly better. Clearer, less harsh, warmer and more defined.
After eq and tweeter positioning the results are outstanding but why?
I am a very firm believer in tuning. I've spent the last 25 years of my life practicing it. It can make decent equipment sound very good and great equipment sound amazing but it can't eliminate a speakers sonic signature. No matter how small it's always there.