Level of difficulty in my opinion goes as follows from least hard to most difficult. The knowledge carryover is significant, but there are absolutely nuances in razor honing vs knife honing that actually hinder the learning curve as well in my experience

-honing a knife to an acceptable edge
-honing a razor to an acceptable edge
-honing a razor to an outstanding edge
-honing a knife to an outstanding edge

I think there are a lot of folks who think they can get a knife to a great edge, and are actually getting what I would consider an acceptable edge. getting a knife to an outstanding edge takes skill and experience beyond what most people care to think about