Do you conclude from "language corruption doesn't necessarily produce poor communication" that "it doesn't ever produce poor communication?"

No, I conclude that from the fact that I know of no language that, of itself, leads to bad or poor communication.There's another trend that historical linguists have noticed about language change. The language tends to keep changing to make it easier to speak and communicate. For example, the inflectional case system did not simply disappear from Old English and Latin, they were replaced by fixed word order (and, at this point, somebody usually mentions prepositions, but they were used in the case system, too). I'd say poor communication is possible in any language. I have never seen a language corrupt. What does it look and smell like?

Ceci n'est pas un seing.