[koz_]

The author of the code is going to have to discover how these APIs work somehow, right? Why would the code end up worse if the author has access to a particular tool for interacting with these APIs? A shell and curl is a REPL for interacting with and exploring HTTP APIs but I don't think anybody would claim that the use of such tools makes code written to those APIs harder to follow.

In fact, one of the benefits of your REPL being integrated with one's editor, and being in the language of the system, is that the kinds of ad-hoc scripts you write when doing exploratory / debug coding which one would typically discard after use can often times simply be committed, either as utility functions or test cases. Far from pulling up the ladder on devs who come later, having a REPL makes it more likely for them to have access to the same tools used to build and understand the system in the first place.