Re: So one remainiac commissions a report from load of other remainiacs...
And that's the point. The Leave campaign's predictions were about the effects of Brexit, not the effects of the referendum. And so is this report.
We've already seen the effects of the referendum: a large drop in the £, which also means that the stock market hasn't gone up in real terms. And many companies preparing their exit from the UK. This report is about what will happen in 2019+.