I can’t give an exact number, but I’d guess that about 99% of Christians (including all the Mid-Acts Dispensationalists who do understand that there are two Gospels but who aren’t Biblical Universalists) have actually been saved under the Gospel of the Circumcision rather than the Gospel of the Uncircumcision (also known as Paul’s Gospel). Simply put, if you aren’t a Biblical Universalist, you can’t be in the church called the body of Christ because it means you haven’t fully understood — and hence haven’t truly believed — Paul’s Gospel. But if you do believe that Jesus is the Christ (Messiah) and the Son of God, and that God has raised Him from the dead, you might be in the church called the Israel of God (or perhaps at least might be blessed alongside the Israel of God, in a manner of speaking, if one is a Gentile).
The thing is, while salvation for those saved under the Gospel of the Circumcision is simply based on faith in the identity of Jesus Christ (as opposed to the faith that those saved under the Gospel of the Uncircumcision have, which is in the finished work of Jesus Christ, and this includes the guarantee of the future general salvation — meaning immortality and sinlessness — of all humanity because of His death for our sins, burial, and resurrection on the third day), Israel’s sort of faith must be followed up by good works, including water baptism in the name of Jesus Christ, and following the parts of the Mosaic law that are still applicable to Israelites today, if they want to keep their salvation (and Gentiles saved under this Gospel would presumably have to follow up with good works too).
Because, yes, salvation is by grace, through faith, apart from any works, but only for those in the body of Christ. And if you aren’t a Biblical Universalist, there’s zero possibility that you’re in the body of Christ at this time, which is why you do need to do works if you aren’t going to become a Biblical Universalist (not that members of the body of Christ shouldn’t do good works as well, but they aren’t required for maintaining our salvation the way they are for members of the Israel of God, since members of the body of Christ can’t lose their salvation the way that those saved under the Gospel of the Circumcision can).
To put it simply, if you aren’t a Biblical Universalist, you need to stop using the Uncircumcision writings (meaning Paul’s 13 epistles) for your doctrines (aside from a few passages in Romans that actually are relevant to the Israel of God) — because his writings are pretty much only for the body of Christ — and stick with the Circumcision writings for your doctrines (meaning the books of the Bible that aren’t Paul’s 13 epistles).
And yes, I proved all of this from Scripture in my (free) Biblical Universalism eBook, so please read it if you have any doubt about what I’m saying, because your “eternal” life (which is a figurative term in the less literal Bible versions that just refers to “age-pertaining” life, meaning life in the Kingdom of God during the impending ages, prior to the end of the ages) very well might depend on it, even if your ultimate, general salvation doesn’t (and if you haven’t studied the Bible carefully enough yet for that statement to make sense to you, it means you definitely need to read my eBook).