There is alot of truth in this article but fundamentally it is a moral discourse and here is why (although my arguments are written within the context of the UK EU referendum they still apply) .. Sorry for long post!
If anything Brexit will precipitate the reformation of global trade and as such the analysis that Brexit will be detrimental to UK gdp by reducing the uptake of trade agreements has no scientific understanding of flow system dynamics aka constructal law, thermodynamic laws and laws regarding self-organisation which states that systems will aways try to increase their flow capabilities. For example, the global proliferation of custom unions is simply a part of this process of increasing flow capability within our increasingly global system but they will dissolve as global harmonisation deepens.
At the point of dissolution, what must be considered is the most appropriate scales of governance. I believe these to be a global regulatory framework in which independant 'national' states coordinate their activities. And I say 'national' states because this scale is more manageable to mediate democratic relations in relation to bioregion carrying capacities as opposed to 'regional' states which in my opinion are too large and so tend towards centralisation but I might be wrong.
In my opinion this relationship between the national (as opposed to the regional) and the global is the right way to increase flow capability and one which should be based on 'fairness' as opposed to 'freedom' in order to fulfill the natural rights to life, liberty and the pursuit of happiness for both humans and nonhumans alike.
Therefore in this context, Brexit is mostly progressive in its intent especially if the global regulatory framework was based on 'fairness' as opposed to 'freedom' whilst it could be argued that Bremain is regressive to a degree but there are understandable reasons why. Bremain may reflect that global harmonisation is not quite there yet. Similarly it might also reflect the current competition between 'fairness' and 'freedom', which not only traverses both the Brexit and Bremain camps, but also traverses Europe and the globe even.
However, bearing in mind that most of Europe is in economic turmoil and UK growth has just dipped to 0.4% which I would argue is due to the moral deficits that naturally form within open market regimes based on 'freedom', perhaps now is the right time to facilitate the next level of self-organisation but one that embraces 'fairness' as opposed to 'freedom'.
If this is true then Bremain and Co are either holding back out of selfish self-interested reasons (i.e neoliberals like Cameron et al, the IMF, the OECD and other free market advocates like the Guardian) or are holding back out of unselfish self-interested reasons in that they are afraid of change in that they fear 'fairness' will be upsurped at the global level in favour of 'freedom' and so are being cautious in their outlook.
However, I say take the leap in the light and enable independant national sovereignty within a global regulatory framework that is explicitly based on 'fairness' and the protection of natural rights for all beings in so far as they can be mediated to produce fair outcomes.