I have a workaround for this problem. I'm sure that there are others who do the same, but I haven't heard it mentioned in this discussion:
At the point along my preferred route which is the farthest deviation from the route that Waze always suggests, I create a favorite, either with a street address, or by tapping and holding on the map at that point. The next time I want to take MY route, I choose my usual destination, wait for Waze to plan the route its way, and then "Add a Stop", at which point I enter my off-course favorite. In most cases, Waze will then map out the whole route the way I like it. It's an extra step, but it's effective, and sometimes this approach has helped Waze to finally see it my way, apparently since this is causing Waze's routing servers to actually calculate my entire route, rather than only the portions of it that are left when I have refused to follow its suggestions.