Brexit is no doubt a factor in easyJets reduced profitability, but not the whole story by a long way, they have also lost load factor, LGW delays, French ATC, Sharm the list goes on add terror attacks in France, Turkey and boat people in the Greek Islands, pick what every you like, having said that these issues affect many airlines, meanwhile Ryanair and Norwegian are showing volume growth and increased load factor.
EasyJets cost base is I suspect higher than either of the above