That's like saying all BT headphones sound the same.????
You do realize that with bluetooth you are bypassing both the DAC and the amp and just using the DAP as a transport (and using the DAC and amp from the car). Your phone will work just as well and sound exactly the same (if using the same BT codec).
Different BT implementations, bt chips, boards, antennas, parts and/or devices can affect output quality.
I was verifing that this new device sounded similar or better to what it was replacing. Especially given the Wifi issues.
My old Granbeat DP-CMX1 sounded noticble different than my Onkyo DP-X1A over BT in the same car, same app, same song. IMHO.