During various updates over the years, Tesla adjusted loudness’ and/or levels of bass/treble response much to the detriment of overall sound quality.
In 2017, there was an issue with sound settings resulting in any owners losing Dolby, having to pump volume to 9/10 to achieve the same loudness at what was previously a 6/7 volume, max bass and treble resulted in less response.
After a number of complaints, Tesla finally re adjusted the levels back after initially stating it was for protecting the longevity of the system. Many complained it was unethical to reduce functionality after purchasing. (At that time 2017 and prior, UHDef/Premium sound was an optional purchase).
I will admit the sound produced from my 2018 MS UHDef does not sound as deep/high as my 2016 90D did yrs ago. Again could be Tesla internally adjusting settings to limit max output..who knows.
Get a 3rd party amp and sub and see if it helps!