Your assessment of what may be causing the autopilot issue is far too simplistic. X-Plane has a LOT of interaction between systems, and the Saab is highly modified to provide even MORE realism. X-Plane v11.10 may technically be considered a minor version but it was definitely not minor in regard to the flight model changes. There were a significant number of changes made by Austin to the engine model and in moving to more vector based math for the flight model. Interestingly, as far as I know, there were NO changes made to the autopilot system. So,the autopilot issues have be related to another system that is interacting with the autopilot. Debugging these types of things can be rather complex and it takes time. Creating a completely custom autopilot would be a MAJOR undertaking and completely unneccessary as everything was working fine in 11.05 (as you stated). in developing aircraft it is much smarter to stay as close to the default systems as possible if they can provide a realistic simulation of a particular aircraft. It reduces the number of things that can go wrong with each X-Plane update.
Personally, I would much rather have a situation where we are getting an updated and improved flight simulator on a consistent basis rather than one where changes are not made just because something might "break". Even the default aircraft have to be modified when flight model changes are made, it just comes with the territory.
Let's be patient and not jump to any conclusions. We will get this sorted out.