This is great stuff, and might explain why for instance New Zealand is pretty smooth right now. (Not a lot of airspace areas).
I wonder if there is any correlation to the DEM/terrain mesh level of detail in these areas. For example, does the terrible performance correspond to airspace boundaries in areas that have received a World Update with the more detailed DEMs? Perhaps the “Manipulators” thread is mapping the geometrically defined airspace data from the nav data onto the mesh defined terrain under the aircraft (to create an “are we in this airspace” flag) and having more detailed terrain means more points it has to look at at the edge of each boundary?
For the “non airspace related” part of the performance problem - I saw a post a while back by someone who was fixing the terrain spikes pre-WU3 where that person said they thought there were terrain post-processing algorithms running on our local PCs.
With the cloud driven nature of the sim this made 0 sense to me - why make 2 million users reprocess the same terrain data every time we fly, just process it “in the cloud” so it’s ready for the sim to consume. However, we saw the first glimmer of some of these performance issues after WU3 where they “fixed” the terrain spikes and the “water creeping up the coastline” issues (by making the costlines in many areas look like someone had taken a clay working tool and pulled them back from the coast).
In addition to the airspace related items, maybe the “Manipulators” thread is constantly reprocessing the terrain mesh that is downloaded from the servers to smooth out spikes and “pull back” coastlines. This would also explain why turning off Bing Data and using only the lower LOD terrain mesh on your local HD improves performance. If so…they should really process this data once before it is ingested into the Azure servers, and not make us spend our PC resources to process it on every flight.
Edit: All 3 of the Class C boundaries mentioned by the OP are in the 2m DEM area per the map in [RELEASE] Release Notes (1.11.6.0) World Update II: USA Now Available!