FR don't use the 189 seat capacity of the 737-800 out of LDY due to runway restrictions, so it won't be as many as 1890 seats each way/week, more like just short of 1500. Still an awful lot though comparted yo Loganair for sure.
One can only speculate the route is doing well as FR have made it daily for the summer (if their timetables are to be blieved), perhaps with the tourist season in mind. I was in Derry over New Year and there was an awful lot of Scottish accents there!! (you notice these things in Norn Iron after years of having no real tourism!)