Trade is bi-lateral. The UK’s trading partners were also harmed by their decision to leave. Short term, it’s just simply a net negative for everybody. Long term (decades), the UK will have a long run growth rate lower than the rest of the EU. Granted, our lack of a crystal ball means that we can just debate outcomes ad nauseum.
But compared to neighbours it's pretty close?
I was against Brexit, but I don't think the apocalyptic predictions have been borne out at all.