Final Cut is a very old product (1998). The entire market for digital editing has expanded greatly since then.
We don't know because Apple doesn't report it, but I would surmise that Final Cut has had a consistently growing user base.
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.
A very important percentage. E.g. Final Cut used to have a 60% market share. Now it's may be 25%?
There's most likely a dip among every other category of professional users.