I do essentially agree with what you say above, Carlita (in relation to loverofhumanity's view of other faiths). I'll leave loverofhumanity to continue their defence of their view (forgive me, I can't remember whether you identify as a 'he' or a 'she', loverofhumanity).
I'm a humble he. I know you don't accept Baha'u'llah but it's the principle that I agree upon.
The Quran clears up misconceptions Christians have about their Bible and corrects some wrong teachings taught them by their Church.
Did Muhammad have no right to do that? Of course He did because He was a Prophet of God regardless of whether Christians accepted Him or not. The Quran makes these corrections and Christians reject them but that is not to say Muhammad is not connected to Christianity because the Quran says the Torah, the Gospels were all from God. So God has a right over these Holy Books does He not?
But free will means the Christian priest will not accept Muhammad so that is understood. Yes Christians may resent being told they are wrong but God chose to say that in the Quran and He is God. Who's to question Him?