SSDs from my observations tend to work well with large blocks of data rather than the small size blocks we find with the assets.
With another simulator I use, I have 196,000-plus installed local assets. These are tracked within a single database, not placed in a single file, but because they are indexed they load up quite fast considering the huge number of assets. On any given route, as they are called since this is a railroad sim, there can be 3000 or more assets which are referenced in the data. A route as large as some of mine, about 250 miles or more long, can take about 3 minutes to load with all assets in place.
The company originally placed the built-ins in single files, however, the load times were not as efficient as listing these as individual assets referenced in the database. The problem was the huge amount of built-ins, close to 8,000 assets, had to be compressed due to the large file size of the single file, and this caused much longer load times and difficulties updating the built-in assets.
