Ok it's taken a good half hour, but there's nothing on any of those routes that is jumping out at me there.
My only suggestion would be, go the way you think is best with Waze running, let it keep rerouting and at the point where it starts following you the way you want, drop a Map Error report, as this will probably be the point where there is an error (if any).
It could be that even with the M6 and Toll backed up, Waze's algorithm isn't accounting for other possibilities because of the "importance" of using supposedly faster roads like motorways.
There are some URs in and around these routes, but I don't see any that would affect routing. I would say it's a lack of data, but looking at the number of GPS tracks around there, it's definitely not that.