I have a Pixel 2 and can use Waze while using Android Auto, and it runs smoothly. Android Auto also runs fast. I can listen to Pandora, Spotify, and the Sync music (AM, FM, Sirius) while using Waze in AA. And it all runs fast... However, it is very buggy. Sometimes my phone calls get fuzzy/staticky, sometimes the radio will not go to AA when I plug the phone in, and sometimes it dumps me out of Android Auto while the phone is still plugged in. Also, sometimes my music coming through AA sounds terrible (low bitrate with no bass). I would say it works well about 75% of the time.
Last note, I was using OBD2AA for gauges on the screen from Torque, and CarStream to stream youtube videos to AA. It was awesome. The kids had music videos when they rode with me, and I had gauges when I wanted them. AA released version 3 (not Sync 3), and it broke the ability to stream video. Most people downgraded to V2.92 and turned off auto-updates, and it continued to work. Google however, pushed a backdoor update (hidden, forced update, that was not an AA update or an Android update), that stopped it all from working regardless of what version of AA you are running. Since that happened, the whole thing seems to be buggier. I was going to root my phone and install a different kernel and rom to see if it would fix it, but I haven't had much time.
Here is the video of when it was working.
https://www.youtube.com/watch?v=eOIp0q2qz3U