and yet with all the presumed abuse (what are you referring to exactly, no tariffs to trade?) GDP, employment, exports, house prices, etc... were not catastrophic.
Some years went positive, some not. For some people in some regions things have been very difficult, for others they are great.
If leaving the EU means erecting barriers to trade so as not to allow cheap imports from China and protect all sectors of industry then the policy should be explicit from the start and fight it under a communist manifesto.
Conversely, if "leave" means no rules and unfettered capitalism, again the policy should be clear from the outset.
You are assigning causality from one factor - belonging to a club - but it doesn't hold. If it were true, all countries should be doing dramatically worse because of the club.
Here is the UK's GPD growth 2011/2015
United Kingdom 2.0 1.2 2.2 2.9
not great, but not bad either.
data.worldbank.org/indicator/NY.GDP.MKTP.KD.ZG
Some indicators make the UK look even better, (house prices) some not so much (debt per capita).
data.worldbank.org/indicator/NY.GDP.PCAP.CD
And by the way, here are the British commisionners en.wikipedia.org/wiki/List_of_European_Commissioners_by_nationality#United_Kingdom