It surprises me that it's built in Python (as is AWS'), which doesn't seem like a very appropriate language for exactly this reason. Go would seem much more apposite.

These CLIs are just thin request clients a la curl. The code execution time is peanuts in comparison to the request latency

It's not negligible versus a single request. Even `gcloud --help` takes over a second on this machine - actually getting it to do a simple list request takes almost no time longer over any reasonable connection.

Plus Python is notoriously not easy to deploy for - a Go (or Rust or whatever) binary would have almost no dependencies to worry about.

The execution speed of the language the CLI is written in doesn't matter. Any difference is dwarfed by the slowness of network calls, specifically their API response times.