Christians are not monotheist. 1 does not equal 3, the idea that 3 can be 1 in unity is known as sabellianism which the early church professed (as well as certain current denominations) when it dumped monotheism. Their are trinitarian and sabellianism Christians, but no monotheistic ones (aside from the few unitarian churches are almost to small to figure in). The historical development matters because it just goes to show how the bible is irrelevant to debate with because its own followers mess up on the very principles of doctrine by combining elements of paganism such as the trinity. Now do Christians see it this way? Absolutely not and fight tooth and nail to say that they are monotheistic but the closest thing is sabellianism. I mean its not like the Christians don't have a history of changing concepts without biblical authority and finding non scriptural resources to back it up (4th commandment rings a bell here).
Apart from the last couple of sentences, that's literally a copy-paste of your last post! You're not adressing any of the points I raised in reponse to it.