"Why so? There are 27 other countries in the EU, most smaller than the UK, but 170+ in the RoTW. While many of those 170 are tiny with no money there are plenty which are big enough to be good trade partners."
Indeed, but since 163 of those countries have trade agreements with the EU, we are ALREADY trading with them.
So unless those last 7 are going to be a major change, no real factor there.
Now if EU regulations/trade agreements are preventing some massive trading advantage, I'd love to hear it. But all I've seen are some fairly petty suggestions, minor agriculture isn't going to make much difference.
But once we leave the EU, we no longer have those trade agreements. So we have to negotiate with each and every one of them. If you think the EU negotiations are hard (and whining about EU playing hardball is ludicrous) wait until the USA and China start in on us.
And you can't blame the EU for it either (I know this is the norm) as they have been quite happy to just carve off a UK sized chunk of the current trade agreements, and everyone keeps the current arrangements. Turns out that no-one else at the WTO agrees.