I linked to the OBR and I find their statements interesting because they're saying the UK's productivity will be 4% lower than if the UK remained in the EU. You say the UK had productivity problems while the UK was in the EU. Let's assume for a second that's true. Then what the OBR is saying is that there is an additional factor negatively affecting British productivity; that factor is Brexit.

Also I think closer ties with Europe would be good because a united Europe can more effectively stand up to big global powers like the US, Russia, and China. I don't want to see the UK bending over backwards to accommodate Trump and his illiberal colleagues. Europe together has real weight to push back against the US. E.g. if the UK alone were to tariff American goods then it wouldn't affect the US too much, but if all of Europe did the same thing together, it would affect the US much more.