I only read up on CLNP based on a fascination with counterfactuals. I will say there is a fair bit to IS-IS and ES-IS that's directly relevant to the original articles points on the circuits-to-bus-to-circuits physical evolution. There was no blanket assumption that the underlying layer look like Ethernet. The subnet equivalent was at a higher level and the assumptions were that there would be an actual network of links to manage.

The fact that IS-IS survived as a relevant IP routing protocol says a lot on its own.