Doesn't matter as much as you imply as we can have trade deals, on our terms not the EU's, with the rest of the world. So our deal with the EU is a little less but we gain by engaging with the world - swings and roundabouts.
Of course it matters.
Firstly because the EU represent roughly half of our foreign trade.
Secondly because the moment we leave the EU (unless we remain in the single market) we instantly lose the benefit of all the trade deals the EU has signed with other countries (more than any other trading block), so straight away we are playing catch up.
Thirdly trade deals take years to negotiate, even if there is a willingness to do so, leading to ...
Fourthly, outside the EU the UK is a far less attractive trade partner than inside the EU. This means we won't be at the front of the queue as countries will be looking to the biggest economies to do deals with - e.g. EU, USA, China etc, not the UK. And as a less attractive trade partner we will almost certainly get a worse deal that we already do in the EU (for those many countries that already have deals with the EU) or that we would have done in the EU (for countries that are looking at trade deals with the EU and also may consider one with the UK outside of the EU).
Wake up and smell the coffee, or perhaps we should call you PollyAnna rather than Jack Knave.