I didn’t see much of a counter to his posts; his challenges were pretty open and specific, and replies to them largely vague and conjecture-based.
That said, the Islamic opinion is derived from specific verses in the Quran, and that significantly narrows the spectrum of opinion amongst observant Muslims.
Regardless, the Qur'an depends upon the Scriptures, while Islam claims it was radically altered, yet it cannot produce the mss evidence needed to support its premise. In addition to problems with Qur'anic mss.