On that page, he asks;
I’d like to hear more from Mark about what he sees as problematic about the current notion of binding. Although the spec seems unusual, the end result does seem to respect WebArch
It does respect Web architecture, but only because it’s read-only. As soon as you need to add mutation support, or indeed any other operation on the same resource, the process fails and what results is not Web-friendly. This is because “operation on the same resource” doesn’t work if the operation is part of the resource name; if the operation changes, the name changes, and therefore the resource-identified changes.
Making something Web-friendly means mapping your data and services into a set of inter-linked resources. Application-specific APIs works directly against that.
And FWIW, from a REST POV the constraint that’s being disregarded in these scenarios is commonly resource identification.