Are mainstream christians delusional and/or oblivious or can they refute this?

Yes. Most Christians are simply not aware of it. That is not an excuse because it does not excuse (the majority of them). I have met a few, people like the brain injured man who had to rely on the preaching of Pastors, that I think God will excuse for what he (could not) read for himself in a Bible. But that is hardly out of the reach or capacity for most English speaking persons. Why Christian leaders ever since Catholicism came into being (about 300 AD) have ignored this fact 99.% of the time is (I believe) antisemitism. But there is a reason for the hard line separation. Jewish leaders after the fall (even before) of the Second Temple are the ones who wished it as much as the early Catholic leaders risen up after the deaths of Peter, Paul, and their immediate students. The term "holy" as in "a holy people" is synonymous with a "set apart" people and often, in both camps (the first 1500 yrs of Catholicism, and post Jesus Judaism) too much emphasis has been on the two remaining separate. To this day, in Israel and the diaspora, only in regards to Messianic Jews does Judaism forget to have any tolerance at all. Rambam did that with his interpretations of Deut. 13:9 which he turned into 5 hate filled mitzvot (commandments). See #37-41 of the 613 Commandments Maimonides supposedly discovered. The peer pressure was just too intense except for in those rare times and places where a Jew accepting Jesus as Messiah was able to withstand both the non-tolerance of Christians to retaining his/her Jewishness as well as the complete loss of all Jewish loved ones for "converting" to Christianity. This is why God, in His Greatness, gave us Messianic congregations and likewise supportive groups. It is also why they are growing. The Church (church being a non-biblical Catholic term) Age never really was though even the most Israel friendly Christian ministries still use it. What has been is the people of Messiah, by languages English, German.....and we are grafted INTO Israel by the spiritual new birth (being born from above) through the process of trusting that Jesus (in English) is the Messiah come, killed in our place, for our sins, and risen, as the only acceptable scapegoat (verses Adam blaming Eve, and Eve blaming the snake, and us blaming...). However, the whole Hebrew roots movement has some serious problems. Too many consider themselves of Israel by the color of their skin. No one, Jew or not, gets into heaven with out being born from above (aka born-again) and that by trust (faith) in God and His Word. Trusting God, as Peter did when he doubted Jesus because he was arrested, returns us to His Son. No Rabbi really trusts God who does not even bother to look at the Messiah and accept him. Christians, on the other side of this matter look far too long at the teachings of their Pastors. That is exactly the same problem Catholics had until the Reformation. Why it did not continue all the way to restoration of what Jesus left when he returned to the Right Hand of the Father until the 20th Century is not to the glory of Christianity. But it is to the glory of God, Most High, that He revived His people again anyway.