I think the author is saying "more complex" relative to higher level languages like Go. They mean to put Rust in the same category as C++. It could be rephrased as "prepared to accept languages like C++, D, and Rust with more complex syntax"

Thankfully that wasn’t implied at all, and it’s not true that rust has more complex semantics (or, I think, syntax, although I could be wrong on that).

That said, it certainly is more complicated refactoring arbitrary data flows. There is certainly a cost for all the benefits! :)