For what it's worth I did 3 years as an FO at EasyJet Gatwick. I've now done about 4 years at BA and am (very fortunately) about 70% off the bottom of the Airbus P2 status list. It is moving quickly at the moment I grant you.
My job at EasyJet and my job now bear no resemblance. People in BA moan as they do in every airline but honestly, my life now is immeasurably better than it was. My biggest problem with EasyJet was the constant roster changes - your life on your days on belonged to the company. I honestly don't know how people with childcare and other commitments make it work if both parents are working. I think in 4 years of flying for BA my roster has changed twice, both times trips taken off me for training.
People stay at EasyJet for a quick command, and that's fair enough. But I think there is a slow shift underway from people chasing money, to people chasing lifestyle. For me, that is why I left. I found 5453 hugely fatiguing and the thought of doing it for 30 years was unbearable. No one really knows yet what flying that kind of roster to 850 hours a year is going to do to your health over the long term... we're the first ones to be faced with doing it for an entire career!
EasyJet is a solid secure job and in the left hand seat the pay is great. But there's more to life than money.