I think philology is a better bet than the Quran, but to each their own. Certainly, the Quran might preserve all manner of folk etymology for Arabic like the buddhavacana does for Indian languages. Folk etymology is not scientifically linguistic, but it is invaluable on terms of knowledge related to the humanities. It tells us how people thought of the language they were using at the time they were using it. I don’t doubt that sakina (pardon my mispelling, diacritics are harder for me on my new computer) has a meaning of bliss similar to “sukha.” It might even be the normal meaning of the term in the present-day and in the Qurannic form of the language. That was never disputed. It was the etymology that was disputed, not the semantics.
The historical meaning of s-k-n in still retained in Arabic terms like
أَسْكَنَ
تساكن
سكنى
مسكن
The last one, maskan, is cognate with the earlier-mentioned mishkan.
A “sutra” is a “thread.” It is a distant cognate with the English word “suture.” The word sounds like “surah,” but they are not related etymologically. Now, suture and sutra seems like a pretty wild stretch, but languages often aren’t intuitive like surah and sutra as words for scriptures or divisions of scriptures. For instance, I just found out that the swe- in the word “Sweden” is a reflex of the sva- that we find in words like svamaṇḍala, svatāntrika, and svabhāva, and it absolutely blew my mind. We have our own sva- prefix in English, but it is incredibly obscure. It happens in the words “suigenesis” and “suicide.”
On terms of the roots, Sanskrit (and Indo-European roots in general) are quite different from Arabic/Afro-Asiatic triconsonantal roots. Afro-Asiatic roots are often in a C-C-C form, with C standing in for “consonant.” Indo-European roots are based on a root syllable, not three root consonants.
For surah, we have “s-w-r.” For sutra, we have “siv.” Knowing “siv,” the Old English “siwian” for “to sew” becomes more intuitive, v/w being a common form of phonetic drift. The Latin “suō” for “to sow” becomes similarly intuitive, but only after the etymology is known. The “v” in the root “siv” is where “sīvyati” (Sanskrit for “to sew”) gets its “v.”