For one example: I believe this is no longer the case, but for a long time 3rd party mapping apps could not display route information on the iPhone lock screen.

Last time I checked, one of my favorite apps for routing me on back roads, Scenic, still can't use my Watch for routing.

Why would your phone be locked while you're driving and trying to use it for navigation? Surely you're not looking down and locking / unlocking it every time you want to look at it, right? You just have it mounted on your dash and it stays on.