Wrong! It would change a lot and would be a real issue, hence why the CEO of easyJet is clearly against the UK leaving the EU.
Comparison with Norwegian is inaccurate. Norway is not part of the EU as we normally refer to, however it is part of the EEA (European Economic Area) and also part of something the UK has always opposed: Schengen Area.
So in some ways Norway is currently more integrated to the EU than the UK!
The threat is not to be like Norway, it is to change things that have taken time and cost to establish.
If the Uk was to leave the EU it would have to re-negotiate its agreements with member states: part of EASA or not? part of EEA or not? etc…,
Companies like easyJet would have to make costly adjustments like possibly: a new AOC, different A/C registrations, different ruling authorities is some areas, new approvals… and obviously hire staff for transition and implementation.
Clearly easyJet would be at a disadvantage, even if only for a limited amount of time, it will be enough for competitors to cease opportunities (Ryanair, Norwegian, Eurowings …).
It would also create uncertainty, and that is not what shareholders want…