Personal Comments:
There are three separate factors that are intertwined in this thread:
- Flight Planning and Routing
- Flight Management System
- Autopilot
1 & 2 are deeply intertwined - the most visible symptom was the earlier “Crazy Ivan U-Turn” defect during IAPs. Working Title solved that one. But you still see other defects - there are many approaches where the Flight Planner is not following published approaches when tied to STARs and creates it’s own unique (and inefficient, sometimes illogical) wide turns involving custom USR waypoints. WT has stated they can’t fully evolve the FMS (the Garmins) without also addressing the Flight Planning and Routing logic, which they intend to do.
Autopilot also has it’s quirks. We still see today AP behaviors which have been somewhat solved by other Mods - for example the rolling oscillation noted on the Longitude and the TBM (solved/mitigated by Dakfly and Mugz). But others - such as random disconnects, still persist today.
Finally, there is what I call the dice-roll factor: the NavData itself. Notably, NavBlue by default is less complete than Navigraph, yet both of them are hamstrung by the fact that there are (by Richard/NG’s count) a little over 2,000 incorrect airports (some major) with completely incorrect or missing runways (as defined by BGLs inside the sim itself) - which means no matter whose NavData you use, the Flight Planning and Routing logic will never be able to use the SID/STARs or IAPs associated with those incorrect runways, so you have discontinuities in planning and complete absence of otherwise valid runways, departures and arrivals.
In short, you can go round and round on this question. The real question is - which of the above are you asking about? The answer is - you can’t ask just one without determining the effects and interactions of the other factors.