Except that to run those in the first place you need to be running non-private spyware on your phone (iOS or vendor issued android ROM), so you give up all ability to maintain privacy in or out of the car.
No, it isn't all-or-nothing. iOS does not leak messages to cars. Just by using iOS doesnt mean Toyota, Subaru, Chrysler, etc suddenly have access to your messages. Using iOS with carplay only is strictly better than using iOS and sharing your messages with the car.