Feels a bit like that's a post-facto argument to me.

It sounds like the Surity thing had "blocks" consisting of a week's worth of documents which got chained together and had their hash published irrevocably every week.

Without the subsequent invention and popularity of the specific implementation of the bitcoin blockchain - I don't think the slow/costly consensus "feature" could be considered a requirement to distinguish between "hash chains" and "block chains" like that.

(But I'm regularly on the losing side of nomenclature arguments - I'm still pissed at all the people who've decided they should call my non-autonomous quadcopters "drones"...)