The Economist’s argument is limited to machinery firms in the Economist’s country. We don’t know whether protection “rarely” allows firms to grow big enough generally. We only know that protection does not allow domestic machinery firms to grow big enough.

We don’t know if ten years is sufficient for evaluating any and every economic policy. We only know ten years is sufficient for evaluating one economic policy that applies to domestic machinery firms.

We don’t know whether or not any machinery firm in the economist’s county has grown “significantly.” We only know that these machinery firms haven’t grown big enough to compete with foreign machinery firms.

We don’t know whether any of the machinery firms in the Economist’s country will go out of business if these firms are not protected from foreign competition.

It is not possible that protection from foreign competition will allow domestic machinery firms to grow big enough to compete since these firms have already been receiving protection for ten years.