The behavior of Waze after it is "switched off" can be verified on a jailbroken phone. There is a UI tweaking app called Springtomize which has a setting that makes inactive apps appear dimmed in the app-switcher that appears when the home button is double-pressed. Inactive, in this context, means no longer using any system or hardware resources. When Waze is switched off, it does appear dimmed down there, which means that the icon is merely acting as a shortcut to return to it as a recently used app, but that it is for all practical purposes shut down. I am not advocating jailbreaking, but just trying to reinforce the opinion that unless some uncommon bug is at work on your phone, you can depend on the switch-off method working as advertised.
One GPS traffic avoidance app which claims to shut down battery draining resources when the app is not in the forefront, but does NOT effectively do so, is INRIX. My bad experiences with that app, and vehement refusal by the developer to admit that what I was experiencing could possibly be the case, is what drove me to revisit Waze, which had been a bit clunky when in first tried it many moons ago. I was delighted to find that Waze had vastly improved in the interim. I've never looked back.