One can follow christ without believing him divine, he also never taught such a thing outright and you are projecting Pauline christianity on to all christian sects even though there are literally christian sects recorded who do not believe this. The gospels don't say a lot of what you clearly consider christian, most of that is in the letters of Paul. Your opinion of it isn't relevant to this and I don't give a damn if you think it makes these sects not christian as I'm not asking for your opinion I'm stating that there are historical christian sects that hold each of the beliefs you say disqualify Islam from being like christianity (which is itself irrelevant to what we're talking about anyway, which is closeness.)
Anyway, you've now completely stopped discussing the main thing we're talking about. That Islam is closest to christianity.
If your conception of what Christianity is fundamentally wrong, there's no point in arguing over how similar it is or isn't to Islam.
To whit:
John 10:30: "I and the Father are one."
Jesus claiming divinity; people moved to stone him for saying this, because he was claiming divinity.
Luke 7:48-49: "Then Jesus said to her, "Your sins are forgiven."
The other guests began to say among themselves, "Who is this who even forgives sins?" "
I could go on with other quotes from Christ, no need for the pauline epistles, but the point is Christ as divinity is not a 'Pauline Gospel,' it is what Christ himself claimed to be.
So yes, those who claim Christ, but deny His teachings, are not in fact Christians, because they defy the meaning of the word. If your conception of 'Christian' includes those who reject the core of Christianity, then it's little wonder that you think Islam is 'close' to it, because you've made the category so broad as to be almost meaningless.
Even then, while Islam could reasonably be said to be closer to Christianity than polytheism, it certainly still isn't closer to it than Judaism. The Torah and the Jewish prophets teach the same vision of God as the Christian Bible does, the Jews simply refuse to accept Christ as the Messiah.
Islam, on the other hand, teaches a view of god that is closer to the (inaccurate) stereotypes of the old testament, a lot of wrath and vengeance, not much Love, grace, or patience. Further, instead of God forgiving man in spite of man's sin, Islam teaches that one earn's God's forgiveness through moral excellence. These are fundamentally incompatible ways of viewing the nature of divinity.
At this point, I feel obliged to ask, what are
your religious beliefs?