That’s definitely a gripe of mine. In general, I actually really like Waze but the silent re-routing really bothers me.
My car’s built in GPS (which is pretty shitty) has the SiriusXM NavTraffic feature that does some basic tracking (nowhere near as good as Waze). It won’t re-route me unless that detour meets a certain pre-set threshold of time saving, and it gives me a chance to refuse change in route before it decides to apply it. I really wish Waze had something similar – basically some combination of “prefer main roads”, “don’t detour unless it saves X time”, and “give me a chance to reject a detour” settings.