"Is a screwdriver + a hammer useful over just a screwdriver?" it really depends what you're doing. Use the right tool for the right job. Writing some low level embedded system? Use Rust. Writing a distributed cluster of services? Use elixir. Need to do something with both, use both.
You can do basically anything in either of them, but they're both completely different systems with different strengths.
A tool is just a tool, don't get hung up on "which one is better".