I think you ought to revise the route-setting methodology!
This is how I do it ...
Let's say that I want to get from A to D via B and C. I start by drawing straight lines on my giant digital OS map between A and B, B and C, & C and D.
I then zoom in to see what roads are close to those lines and also to see if the lines go though any built-up areas. If the roads look a bit busy or the lines take me through congested areas, I would look at the map and decide whether to put extra 'via' points in to create lines over more promising-looking territory.
A few iterations of that process and I have the basis for my route, away from most A-roads and town centres.
The final stage is to choose the exact route, taking into account whether I want to stop anywhere e.g. a shop or cafe, in which case I would make sure that there were shops/cafes where I wanted them.
So I would be thinking 'why go through Milton Keynes', 'why go through Rugby' and so on, and route around them.
There can be 'gotchas' like major rivers to cross with few bridges, or maybe one-way systems.
My final check is to use Street View to check anything that looks iffy. If the Street View car couldn't get down the road, then I probably wouldn't try to either. (Obviously, towpaths and cyclepaths are exceptions but I wouldn't end up on those by accident!)
