Arguing that Brexit is not as bad as a pandemic is super weak.
I'm making the point there are more important economic problems right now.

We're not going to run out of food. Stop being hysterical. Not because of Brexit, not because of covid. We might run out of brie, or Choco Libniz, but we're not going to run out of anything that comes from Brazil, or any of the many non-European places much of our produce already comes from.

The point is the smaller we get the weaker and more isolated we become.
This is a matter of opinion. There are subjective terms. Weaker? If we're forced to buy British because it's now cheaper than imports, that is good news for our producers. Where there are tariffs there are opportunities for those not subject to such tariffs, such as those trading in internal markets. So while you think we're weaker, I think we're stronger. And isolated? Again, subjective. We were already isolated, our "influence" has been in decline for many decades, throughout our entire membership of the EU and EEC. We've been isolated from Europe through our foreign policy for a long time. So it's kind of meaningless to talk about being "isolated" when everybody already hates us.

except that their economic interests are pretty much identical to ours
Not at all. Not. At. All.

If this were true, then we would have equally performing economies. But we don't. The British economy has been sluggish compared to Germany, pretty much since the end of WWII. Somehow we paid a higher economic price for that war, and they are still stronger than we are. They have bought up a large part of our car industry which has had positive economic benefit for Germany at the cost of British jobs. So no, our economic interests are not shared.

The covid shock will be short term, no-one expects a great depression to result.
This seems naive. Covid is global. Brexit is not. Brexit won't cause a global recession, but covid will, and that of course impacts upon every economy in the world. I think a great depression is exactly what is coming, and is probably expected by those who work in finance. idk, but I can't see how we avoid it. Every country has been affected.

The vaccine will get things going again, but many people have lost their jobs, much money has been picked from the magic money tree to keep things ticking along, we'll be paying for this for at least a decade in the form of austerity.

Brexit is something business has been expecting for four years now. Contingency plans would have been made. There is opportunity here as well as risk.