We had a Renault Kadjar hire car whilst in France last year which had CarPlay, never had the fuel go low enough to prompt a warning but if you used the built in sat nav or via a CarPlay app it did show some directional arrows and distances on the dash behind the steering wheel as well as on the main screen. Was quite handy.
The hire car Vauxhall i had would show music stuff on the info screen behind the steering wheel if it was from the radio or streamed via Bluetooth but if you played anything via CarPlay it was blank. I think basically Vauxhall did the minimum to implement CarPlay. As an aside was playing about building a Volvo estate on their website configurator earlier....£300 option for CarPlay\Android Auto to be enabled on their infotainment system!! I'm at a point now where a car not having CarPlay would be a bit of a deal breaker, be an interesting test for the salesman to see if he was happy to let me walk away from a £30k to £50k car over £300 to enable it.
Believe it or not, everything you said is true for most cars. Most do not implement all the features they can. The low fuel warning is the only one I’ve ever seen.
My year old VW Atlas only gives me the low fuel warning in its own nav system, not CarPlay.
I just wish car companies would embrace CarPlay and Android Auto as enhancements to their systems instead of offering much worse options just to “stay on brand.”