I think the Clojure version does have some actual improvements over the Bagwell version, and some implementation tricks improvements as well. But I don't remember all the details.

Well, sure. But it is not like Hickey invented the 5bit partitioned trie (there is work in sml and Haskell before that), nor did he invent functional tries.

He took what was a research topic and made it standard. There were no other 5bit partitioned tries in (wide) use. I think he did that in a way that signals a fantastic sense of taste, and if you are implementing a programming language you need taste.