It's all very well for a group of economists to express the opinion that we would be better off if we were free to trade with anyone . . . but they aren't the ones who have to negotiate the trade deals.
Hypothetically, yes, I would 'kind of' agree. If we were free to export to any country in the world without tariffs, that seems really good . . . but then, would we really want to allow unrestricted imports? . . . what about stuff like Chinese Steel?
In reality, politics is very much a part of the equation and that means complex trade deals with some give and take; so no, an economist prediction taken in isolation is not really very helpful because they have no idea what the final terms might be.