Apple-to-Apple seems to be dead reliable from everything I've heard. Samsung-to-Samsung seems almost as good. Apple or Android to random, Chinese car stereo might be a connectivity nightmare. Connecting to an OEM stereo with whatever implementation was poorly specified by the car company might also be a nightmare.
We have two cars from the same manufacturer, each paired with two iPhones. Start either car or drive by, and the car will take over an existing Bluetooth connection from one of the iPhones. And by take over, I mean: disconnect an active connection streaming to Airpods/Beats/Airplay soundbars, and grab that stream of music/video/conference call into the car.
The driver in the car then has to pause playback or hang up on someone else's call, because there's no way to pass it back.
Bluetooth as a network protocol, that might be stable. Bluetooth interactivity is not stable or even usable in many cases.
It's not just in cars and other non-computer interfaces, good luck trying to pair a non-Apple device with an Apple device. If you say "it works on my computer", congrats, you're the only one. And also speaking hyperbolically.