Thank you for reaching out. This forum is monitored by a group of volunteers. I'll do my best to answer your questions. Others may jump in to help clarify.
Please submit your app suggestions at https://support.google.com/waze/answer/6276841
. We can only fix map issues through this forum.
Waze routes on traffic speed data. Avoiding certain road types is an all or nothing option. If you say avoid highways, Waze will do just that even if it means significant detours. There is no shortest route option any more as most users want to get to the destination as quickly as possible.
Since Waze is always trying to find the fastest route, it will continue to route you back to the original route until it is faster to take an alternate route. If you know how you roughly want to go, detour and ignore the reroutes until your way becomes the fastest. If there is truly just a few minutes difference that will happen quickly.
There is the option to see alternate routes in the app. Once you've entered your destination and the fastest route is calculated, tap on the ETA at the bottom of the screen. Then tap on Routes. That will show you the two next fastest routes in addition to the fastest route. You can tap on any of them to choose that route. You can also do that at any point in your trip.
I hope this helps explain what's going on. Let us know if you have any other questions.