From
their schedule the average block time to me looks about 2 hours, probably the same or higher than FR (all those Ireland-UK 50-60 minute sectors...)
737s are entirely reasonable for those sector lengths. So whatever about "thin", certainly not "short".
However what is noticeable from the schedule is that with the exception of STN-WAW, all their routes were served a *maximum* of once-daily. That could have been because they were too thin for more frequent service, or it could have been because the airline felt the need to stake out as much territory as possible in the face of expected competition, but it does look as though their fleet was spread a bit thin. This also means of course that their marketing budget had to be spread across more stations.