In Cloudflare's case, Rust is much more productive.
Rust modules can handle any traffic themselves, instead of a split between native code and Lua that is too slow to do more than config (Lua is relatively fast for a scripting language, but on the critical path it was a "peanut butter" slowdown adding latency).
At the size and complexity of a server serving 20% of the Web, Lua's dynamic typing was scary. Modules in Rust can enforce many more requirements.
Rust's solid dependency management also helps share implementations and config logic across modules and even different products, instead of everything having to go literally through the same server.
Do you by chance work at Cloudflare, who has migrated away from Lua to Rust?
Curious to hear observations on productivity hit going from Lua to Rust.