I think one of Clojure's main strengths for concurrency / parallelism is structural sharing of immutable data across threads, which you simply cannot do in Erlang.
I kind of agree. Erlang took the "share nothing" thing to extremes by copying everything which, while improving memory safety by a huge margin, introduced (a) various GC footguns (like the shared big binaries gated behind refcounting which is a famous footgun for very long-running apps) and (b) reduced its raw speed.