I generally agree with your assessment but not totally. The mids are actually very good if you balance the system properly. I did add a powered sub for the bass falll off that Bose puts into this system, but that was relatively cheap. I listen to mostly classical and jazz and find that the response is relatively flat. Before I added the sub, I also got fall-off on the highs. Many people compensate by pushing up bass and treble levels significantly, but that is a mistake as you will dull the mids. The woofers in the doors do put out some mid-range but their location is not good for sound staging those mids. The problem with Zeppelin and other early rock bands is that they were experimenting with electronic music and playing with left and right channels because all we had in those days was stereo and not surround sound. Orchestral, jazz, and pop and most other music play to center stage. Since I don't listen much to older rock, it certainly doesn't bother me.
Balancing the system is important. To get adequate sound staging of the mids you'll have to set the fader partly to the rear. That works really well on the hatch given the location of the rear speakers but I don't know how it works on sedans.
Sound staging is extremely important on this car. You hear separation mostly on the high frequencies and if your system is not balanced properly you'll lose some of the stereo effect. That was my problem before adding the sub. Even though the LOC manufacturers will tell you that they don't pull much from the line, putting in the LOC (and I used a high quality AudioControl LOC) will slightly reduce the output to the woofers and bring the soundstage higher so you hear more highs and thus more separation.
I'm particularly sensitive to clarity and flat response, and what I get now is almost as good as the $3,000 system I had in my last car. While the clarity was good prior to the sub addition, I was not happy with the sound staging, highs, and bass falloff. The AudioControl LOC has very good compensation for bass falloff which is why I chose it.
It cost me $200 and several hours of my time to upgrade this system, both for installation and balancing, but it's really great right now.