It would be way more convincing if the Arthur used primary historical source documents to justify this as a myth. For example, if he could find an old architect who wrote that the spiral staircases were for aesthetic reasons or for making the climb up easier, that would be more convincing.
Instead, the author argues from almost first principles and bulk observations, which seems to be unconvincing logic in establishing historical intent.
In the article he finds the first written mention of the "purpose" of the spiral going in one direction is in 1902. And explains that this 1902 author was obsessed with spirals and fencing.
I think the fact that there are no primary historical source documents that say "hey, we're building this castle this way just in case it's breached and we have to have a sword fight on the stairs" is one of his main points.
It would be easy to disprove the article author by finding such historical documents. Do they exist?
Instead, the author argues from almost first principles and bulk observations, which seems to be unconvincing logic in establishing historical intent.