Things may have got lost in the translation here I think. Whilst this may not be the reason there have been several French ATC strike/work to rule events recently. ALL operators were told that they had to reduce their planned traffic movements by 20% in various sectors of French Airspace ~(I'm sure someone can dig up the NOTAM). So if EZY
PR say "unable to secure ATC slots" this may well be the reason but is a poor explanation. It does affect ALL but obviously an operation the size of EZY (1100 flights per day) which has a high percentage routing through French Airspace (ALC,BCN,AGP,NCE etc) will be disproportionately hit.
However, EZY's ability to deal with the subsequent disruption is a different discussion.
A4
PS - Very good Jumpseater