There are definitely less flights in the winter than in the summer, but that does not change the LF.
Load factor of A319 at 90% is a lot different that Load factor of a A320 and Easyjet has roughly 154 A319 - 56 A320.....
So based on 153 and 183 seating configs and 90% LF then if every plane in air at same time there would be 30,800 Pax...............with an all A320's fleet and 90% it would be 34,600 pax..............a not inconsiderable difference