EU is a group of small countries that otherwise would have very little bargain power. By creating union small countries like the Netherlands or Latvia have a large behemoth representing their best interests and regulating law between members. The oblivious drawback is that you need to surrender some decision power to a group of random people that might have different interests.

It took 7 years to reach CITA deal(EU - Canada). It might take a decade before the UK catch up with trade deals. Even then it would not be as good as EU deals. Companies are already cutting investments and withdrawing from the UK as we speak.

https://en.wikipedia.org/wiki/European_Union_free_trade_agre...