IOM terminal didn't re-open to passengers until 1100 today meaning the first departure of a based aircraft would have been some time after that - probably an hour at best.
Five hour delay on a based aircraft scheduled to depart at 0650 and finish at 2030 would have pushed its arrival on the last flight tonight until 0130 assuming no time made up through the day, and you more likely lose time than gain it given the handling / ATC / PRM problems out there right now.
Even if IOM would have stayed open to 0130 tonight (which is most unlikely), there would be serious knock-on delays into tomorrow due crew duty hours.
Tonight's EZY LGW delay also looks to be nothing to do with this morning's issues as the 320 in question has flown to SVQ and FAO. It's running late because of a delay to the FAO, not because of IOM security this morning. The FAO delay looks to have been LGW ATC systems failure issue according to the EZY website.
It's not a day for points scoring on any side - it's a mess all round, by the looks of it. Most of it seems to be stuff that no airline can change whether security or ATC.