Its also two things negotiators and knowing your strengths.
The world's best negotiators wont be able help you very much if you do not have much to offer.
Also I am skeptical of your assertion that anyone could write trade deals. It requires a very deep understanding of economics, international finance, geopolitics and a bunch of other topics - I would say being able to be a good trade negotiator is a lot more difficult than being a programmer and has far more profound consequences.
Like I said, I've read trade deals. One I actually read almost from start to finish (the recent WTO deal on upgrading customs rules, I forgot the specific name).
If Chile can sign trade deals with much bigger economic powers, much more quickly than the EU can, I see no reason why the UK would be unable to. Can you justify your assertion that trade negotiation is much harder than programming, or is that just a feeling?
China pursues a mercantilist strategy in many respects. Take steel, for example: unrestricted trade with China would wreak havoc on Germany's steel industry, with potential knock-on effects further along the value chain - and there's no guarantee that China would keep steel prices low after predatory pricing.
No, that does not follow.
I've actually read trade deals. The idea that there's only a handful of people in the world who can negotiate these things is ridiculous.