But in each of the languages that inherited the Chinese rendering of the Heart Sutra -- Japanese, Korean, Vietnamese, and others -- the mantra is pronounced completely differently, by the principles of sound change over the centuries!
In fact, the Japanese rendering is "gyatei gyatei haragyatei harasōgyatei boji sowaka", while the Korean rendering is "aje aje bara-aje baraseung-aje moji sabaha". Each of these is in turn the Sino-Xenic reading of the same Chinese transliteration of the mantra: 揭諦揭諦波羅揭諦波羅僧揭諦菩提薩婆訶.
So I wonder, if you believe in the power of the sound symbolism of the mantra, why was it ever acceptable to transliterate the Sanskrit into Chinese, and from there into a multitude of other languages?
I'd say it wasn't transliteration, it was just writing.
Sanskrit was written with local script throughout the world. Unlike some other languages, which have strong affinity for one script, Sanskrit can be written with lots of scripts (e.g. Burmese, Tibetan, etc.). So Chinese characters were probably perceived just as another way of writing, not as some kind of vulgarisation.
Sure, in the end the pronunciation drifted in unexpected ways. But I think it's not because people used Chinese characters, but because the knowledge of Sanskrit in China, Japan or Korea was not that widespread.
Chinese Buddhist texts are famous in the study of ancient Chinese for often (though not always) being not Classical or at least incorporating an atypically large number of vernacular elements. However, to the article's point, they do often remain difficult to read without an understanding of certain Sanskrit-derived Buddhist proper nouns.
I’m not sure this will hold for all religions, but I think the general thesis is essentially correct. And it made me think about how technology itself ends up shaping belief systems. Without the “technologies” of writing and books, the history of the last ~2,500 years would be very different, religion/culture wise. No Bible, no Quran, no academic methods of analysis which arose out of examining scripture, etc. The interesting question is what the religious artifacts of the future will look like, influenced by computers and the internet.