I'd agree with you there.
From the excavation, they found evidence of iron processing inside and a four-post structure nearby. No mention of a potential earlier ceremonial function.
I am having great difficulty establishing exactly what sort of threat this is supposed to be under - I've even spoken to the chap who manages the site, who asked me where the drains were so he could go and unblock them. The area is managed under a conservation plan approved by all the big wigs - EH, EN etc. They have offered to show me round the site and discuss any issues.
Newton Kyme effectively had a Roman Fort built on top of it, and Catterick had a Roman Road go through it - but they were Romans.
There is some potential evidence of sacred sites being transformed into defensive structures by the Iron Age, not henges that I'm aware of.
I'm thinking of Boltby - this has a relationship with the BA burial monuments of the surrounding landscape but the fort itself is very early BA so may have been defensive from the start.