My reply to your "list" above, is to repeat the obvious. (Your questions show you do believe in Tahreef)
Allah sent a text to guide humanity, He said that all other texts are corrupt except this text, He said that all those believing in the other texts are deviant and astray, He said that ONLY our text is true guidance and that He will not send us another text after it, it is the final text brought by the final messenger and we all became religiously accountable after receiving it.
What happens is one of three things,
1-Either HE protects it from being altered so humanity can always benefit from it since we are accountable religiously. (Belief of Ahlul-Sunnah)
Or
2-He leaves it without protection and thus sooner or later it will be lost and the earth will be devoid of guidance and we become all free from being accountable religiously. (Since God is just and fair)
Or
3-He takes it away from us and gives it to some hidden man who vanishes without a trace leaving the earth devoid of guidance but we are still religiously accountable. (A Rafidi belief of an unjust god)
The first is what any rational devout Muslim will believe, the second defeats the purpose of creation, and the third belief is evil, it is absolute nonsense that only an unjust and unfair god would do. Sadly, some Rafidah have this third one.
The next point is, what is "protection"? What do we mean when we say Allah protected the Qur'an?
The protection of the Qur'an means: The preservation of its texts exactly as intended when revealed, and its availability to the mainstream Muslims.
If any of these two parts is missing then the Qur'an was not protected nor would its existence serve a purpose. If the text is not preserved by Allah then it becomes corrupt and unusable, if it is hidden from the Muslims then it is lost and unusable.
The third and last point is "How" meaning: How does Allah protect the Qur'an?
The answer is that it is none of our business, He promised to protect it and that is sufficient for us to believe in its integrity and authenticity.
By observation we see that Allah made the believers successful in memorizing it, then collecting it, then preserving it, then spreading it in the lands and mass transmitting it to the next generations and this continued generation after generation and that is the Qur'an everyone relies upon today.
Thus Allah chose this system to preserve the text of His message. We do not know of any other system as Muslims.