Amateur question: could it be that all the extra sound deadening material and solidity of the 2015 car is affecting the audio experience? Particularly for the bass?
Might be... In the old Days, when my family elders made their own Klipschhorns (and other EV powered designs) from their kits, fabric made a difference. Also, how the boxes were tuned with the type of wood, and insulation inside.. As an example, booming Cerwin Vega speakers, their enclosures were designed to add the 100-400hz boom. On the graph, there would be spikes, even with "flat EQ" and crossovers. I believer you have a valid point. The doors, back shelf, behind the back seat, bracing, all could affect the tonal quality. And cause spiking in different frequency ranges. Also, the clarity of the speaker drivers for all seem to be not as clear.. Mid and high included.. Could be the digital crossovers, EQ, sound manipulation, or something based on the DSPs in the system.
If one wants to test the tonal quality, find some lossless audio that has instruments.. Piano is great test. So are sax, clarinet, French horn, Cornet, trombone, snare drum, timpani, bells, harp, xylophone, piccolo, tenor violin, cello... Solo, or together.. If you can find real record music, no tuning, that has one or more combination of these that will show a broad range of frequencies, and they are hard to duplicate clearly, you will get a better picture. But then, if you have not heard such instruments live, or on good quality (does not need to be esoteric) gear, your heart will tell you what you are experiencing. Certain female and male singers will also betray lousy tuning, and bad design.. Breathy females with range and dynamic range will crush a bad design system.. Also, Frank Sinatra or Harry Connick Jr will test a system. Of course Michael Blubley, IF one can find a good copy or recording.. Carrie Underwood in at least a CD is not a total disaster compared to today. Compared to the past, a mess.. Tuned to the hilt, compressed, and EQ out of natural norms. If that is all you have, use her..
If you can find the Battlestar Galactica (modern remake) pilot mini series sound track, some amazing modern mixing going on..some of the instruments are a mess, but many are left alone. Plus electronic instruments are decent. I took the DVD audio, and handbrake in some of the scenes. Have not seen a DVD audio of the soundtrack.
I listen to "Turn down for what", Titan "Heart and Soul", Evansence Fallen "Bring it to me", billy Thorpe "Children of the sun" also.. All auto tuned, many times compressed and EQ to death.. Also, just not so good recording equipment. So, I am not some classic only guy.. These also, as modern mash up as they are, sound better in a better designed system IMO.. They still sound better to me in the 2012.
Recommended albums. Get lossless versions of Sheffield direct to disc masters, certain Pink Flloyd versions which have the dynamic range of the vinyl and massive analog tape masters.. Those can be good tests of a sound system too..