When EZY brought in the new handbaggage rule last year they also increased the average pax weights used for the load sheet. I no longer fly for EZY but seem to remember they increased pax weights by 5kg. So the extra load being brought into the cabin will be accounted for.
As far as distribution goes the fact that EZY flies 737 300 and 700 series aircraft which are relatively short means it's pretty hard to load out of balance ( unlike the -800 for example). I would imagine the airbus is similar as it's not that long either. The checked in bags are loaded into the aft hold which counterbalances the fact that more people tend to sit in the front half of the aircraft. In the 18 months that I flew with them I was never really out of trim on ttake off - so the system works!
