I write Rust as my day job and I still consider it a complex language. There's a lot of non trivial things encoded in the type system. Send/Sync, Pin, async/await, object safety, borrowing, ownership, I could go on.

It's also pretty different to what most people are used to. I found it a approach to polymorphism refreshing, coming from Haskell, but that's not a typical pathway. The average Java dev will need some time to get used to how extensive generics are in the language.