Its more a case of operational capacity. 90 slots a week is equal to 45 departures and 45 arrivals per week so about 6 to 7 round trips per day.
The remaining 140 slots that will need to be returned, probably over the next year or so, will equal 70 departures and 70 arrivals per week so about another 10 round trips per day.
I believe easyjet will use more 321s at Gatwick to offset some of the capacity loss.
Apologies to this thread for going off topic.