It actually works in a number of scenarios. For the GT-O overall classification it doesn't matter at all how many are in the Pro category as all contestants are counted anyway. Only the Am-category shouldn't have too few contestants, or otherwise it doesn't make sense.
From last year's grid, I guess it's pretty clear Lout, Yeratel and me would be in the Pro-category, with 1 or 2 others possibly added.
As even FIA's own Platinum/Gold/Silver/Bronze driver categorization seems to have no clear rules and a driver's classification can change from season to season, I think it's wise to treat it with common sense here likewise.