Wayyy bigger, the economic, political and diplomatic ramifications will be felt for the years to come on a global scale. EU will be forced to change, thee will either be a shift of powers or a consolidation of the players in place, Russia will use it as a major play, so will Turkey... Lots of EU nations will wonder "what if", which will cause a lot of political movement...
What just happened is groundbreaking. Exiting NATO, in comparison, is a blip.
Edit : From an European standpoint anyway. But Americans will feel it too, and Trump has already (mis)used it as an argument. UK leaving the EU can be twisted, after all, to fit any and all narrative.
Well it's a huge destabilization, and if there's one thing that investors and banks don't like, it's uncertainty. So so far, that's not good. On the long run it's impossible to say, maybe the EU will sort its shit out without losing too many members, maybe the UK will manage to work it and make it through intact, maybe Russia won't try to take advantage of EU's sudden political weakness...
A lot of shit can go real south real fast, but maybe it just won't.