CI is a continuous integration tool. There are inherent latencies to committing, pushing, deploying to AWS, running tests. Mature development tooling, if it's not REPL-based, will at least allow a local debugger to step through the code compiled/run locally, without these remote latencies.

Both tools are necessary for fast engineering, but in different contexts.

I didn't say that you don't need CI. I use CI regularly, and I think it's best for CI to be for testing, and to minimize the build artifacts except those used for test results.

A lot of developers have this preference for client side code. Since the early days heroku has been building the client side bundles for rails.

The parent’s point was that contributors shouldn’t have permissions to upload binaries; they only commit source code and your CI infrastructure compiles, releases, and deploys it.