It's a bit unreasonable, IMO, to criticize the fact that RDAP communicates using a JSON API -- while JSON is inexorably related to JavaScript (and it's not without its issues), it's ubiquitous on the modern web for serializing data, in any even vaguely REST-shaped API.
You could argue that a more compact, binary, wire format is more appropriate (though I wouldn't, in this case, since for small, simple payloads, I think simplicity and human readability trumps sheer wire efficiency). You could argue that JSON's a poor serialization language in general (which is debatable, contextual, and in this case, I don't think there's a widely-accepted better option).
But let's not act like "a JS-derived serialization format" is some kind of mark of the beast here.
You could argue that a more compact, binary, wire format is more appropriate (though I wouldn't, in this case, since for small, simple payloads, I think simplicity and human readability trumps sheer wire efficiency). You could argue that JSON's a poor serialization language in general (which is debatable, contextual, and in this case, I don't think there's a widely-accepted better option).
But let's not act like "a JS-derived serialization format" is some kind of mark of the beast here.