They lost most of the market for two reasons:
- Final Cut X was a major re-write that didn't support importing old project formats for something like two years and didn't support all required video formats for the same period
- Mac Pro was abandoned, twice. Once for years before the trashcan design. Once for years after the trashcan design.
We don't know because Apple doesn't report it, but I would surmise that Final Cut has had a consistently growing user base.