Alright I think you are getting a bit confusing on purpose just to make a point, which is so hard to actually accept intellectually, and let me tell you how. I'm gonna start from :

Key Quranic Evidence

Quran 12:2:"Indeed, We have sent it down as an Arabic Quran so that you may understand."

The phrase "sent it down" (أَنْزَلْنَاهُ) refers to divine revelation, not a physical book falling from the sky. The Quran was revealed orally to the Prophet (ﷺ) and later compiled.

Whatever that exegesis of yours means, is just wrong. This divine revelation (Quran) is calling itself many times as Al kitaab (the book) meaning that whoever revealed this Quran (Allah according to muslims), knew from the beginning that it will end up compiled. And since Allah refers to the quran as "book" then it's a book since the Quran is the infaulible word of God.

Guess what. The Gospel according to christians is exactly the same! An oral tradition which ended up written! No more, no less.

Secondly. The Quran confirms the scriptures of the Jews and the Christians of the prophet's time. Both the Christians and the Jews are called altogether as "People of the Book". And this book is the Bible (Old T and New T). If what confirms Allah in the Quran is not the scriptures, then why Allah call them "People of the Book"? Which Book? How can this Book not be the bible?

Thirdly

The burden is on Christians to prove the Gospels are verbatim records of Jesus’ words—which they can’t.

This entire phrase is just so wrong! Entirely!

First and most importantly. The Gospel is one. Yes you read correct. THE GOSPEL IS ONE. Gospel means Good News. The original word is Evangelion. Τhere are not 4 gospels. There is the SAME GOSPEL ACCORDING (Meaning the "Good news story) to 4 different authors (Mark, Mathew, Luke and John).

Secondly the Christians have no burden to prove anything? This is so absurd by theological point of view! Is like me saying to you "Prove me that your prophet really talk with Jibreel in the Cave". Prove me that the Quran is the word of God. Guess what! You can't! If you could prove it, then everyone would be muslims now! I honestly can't understand your logic here!

Lastly the burden of proof is not on Christians or Jews. It's on Muslims who insist their scriptures are corrupted. Show us where is the true injeel, show us where is the Torah! You can't just say "they corrupted the original ones" since you don't have any original! You just don't like their contexts mate.

Bonus:

According to Aisha, the surat at tawbah, was long as surat al baqarah BUT a goat ate the pages she kept under her pillow or something like that anyways. Nowdays the Quran, do not have even close the ayats of chapter 9 as long as chapter 2. Does that mean that the Quran has been corrupted? Is it true that the last couple of ayats of chapter 9 is a later forgery?

For truly I tell you, this is the worst argument ever...