The point i'm trying to make is that the maximum take-off distance for the EZY A320 increases in the summer months, making long sector destinations (such as ACE & TFS) inaccessible. The Warmer weather reduces air density meaning take-off distance increases, subsequently this is an issue for SEN's relatively short runway.
I suspect you're right and demand does dip for those destinations during summer, but even if there was demand EZY couldn't operate those routes anyway.