Hello terrier, good to see you back on here.
Re easyJet timetable, there are certainly reduced numbers of rotations for some routes in the winter timetable (compared to the summer) such as PSA, VLC and BUD, also PMI and NCE (these last two as previous winter), some of which you mention. Despite this the eight based aircraft still seem to be fully utilised with, again as you say, such things as a second daily GVA throughout the main part of the winter.
What I was speaking of is the current situation. This week the SXF did not run on Wednesday and the afternoon BFS did not run on Tue or Wed.
I checked the easyJet web timetable but there is no indication of a reduced number of rotations on these routes in Sept or Oct.
But if you try to book BRS-SXF a 'no flights' notice appears for Wednesday 28 Sept, 5 Oct and 12 Oct, but it is bookable again from Wed 19 Oct.
A similar thing applies to the afternoon BFS on Tues and Weds until Tuesday 25 Oct and Wed 26 Oct from which dates the afternoon BFS is again bookable. This is the last week of easy's summer timetable (the winter one begins on 30 October according to their website) so it is not as if they are waiting for the winter timetable to begin before restoring the afternoon BFS on Tuesdays and Wednesdays.
I can find nothing on either the BRS or easyJet websites saying why these flights have been taken out, albeit apparently temporarily.
A broadly similar situation seems to exist at NCL on their SXF and BFS rotations.