I was talking about the compromise, if node is slower it provides better productivity.

Why would a experienced java dev be less productive than a node js one?

Tooling, typing, boilerplate and contrasting to the library that is npm.

Vertx is polyglot, you can use js and npm if you like, so in this respect vertx can be more productive as it allows you too use the tool that works best for your problem, be it npm, maven, gradle or language: java, javascript, kotlin, etc...