OK. You suggested that:
There is an original language before the Babel event. After the event, the original language continued and did not change. Heber is the first one named it as Hebrew.
That is clear and understandable.
But, why is it a must be, or a more reasonable case? How is it different from a brand new language called Hebrew after the event, instead of being an inherited language?
I think it is an important event of redemptive history.
In Ephesians 2, we read that there was a "wall of hostility" between Israel and the nations prior to Christ. Obviously, the apostle says that it was their particular covenant with all the commandments and ordinances that separated them from the rest of the world. Everyone else was outside that covenant community; the nations were alienated from their commonwealth, strangers to their covenants of promise, having no hope, without God in the world. Christ was promised and revealed only to Israel under their Law and through their Prophets. Believers in the OT era were to be found among them, because they had those promises concealed. The Church was hidden in the nation of Israel before the New Covenant, there were believing Jews and unbelieving Jews. What Paul says here, and in Ephesians 3:3-6, is that Christ has broken down that wall so that salvation would extend beyond the boundaries of the Jews into all the world. This is why we Gentiles have access into this faith, not just Jews who had that right first. In Christ there is no Jew or Gentile.
Still, what does this have to do with anything? It was commonly understood that this "wall of hostility" did not just begin with Moses and the Mosaic Covenant, not even with Abraham and the Abrahamic Covenant, but it may have begun in progressive stages up to that point beginning with Eve, then Noah, then Babel, then Abraham, then Isaac, then Jacob.
We read in Genesis 3:15, after the fall of our first parents, God put an enmity between Eve's seed and Satan's. Christ is in that Seed, if not that Seed itself. Genesis 4:25 suggests that Abel, though the younger, was that continual seed, but since Cain (Satan's seed) killed him, she made
Seth to be her offspring instead of Abel (thus his name means "appointed" for this reason as Genesis 4:25 notes). This shows that Seth and his line carried on that promise of Christ, whereas the world remained in darkness. Then we read that Noah was righteous in his generation, a direct descendant of Seth. He was to carry on that promise. After the flood, we see Noah cursing Ham's son, Canaan, for what he did when Noah was drunk. But, he says in Genesis 9:26 that God is with Shem, and prophesied about Jepheth dwelling in the tents of Shem. What does that mean? It has to do with Christ, in Shem's seed, or who is Shem's seed. The world will take refuge in Christ. Now we see an enmity between Shem's line from the rest of the world. Them we read about Babel, and Heber being the father of the Hebrew race. He is a direct descendant of Shem. It is possible that he didn't consent or join hands with the men of Babel. God scattered them across the world with their own diverse language, but continued to reveal his will and salvation in Christ to Heber's line. Heber still spoke the language of Noah. Now, in Peleg the church of God was hidden in is line. Babel further separated the church from the world with dividing the languages, leaving the Hebrews by themselves. Then we read about Abraham and him being called out of paganism to be the father of a multitude of nations through his offspring. Isaac's line was separated from Ishamel's, Jacob's line separated from Esau. Israel became the very center of those promises regarding Christ, there was no hope and salvation outside them. When Christ came, he abolished that enmity and calls the world to turn to him to be saved.
I think this is the reason why Hebrew was important to have existed prior to Heber in this discussion. I briefly touched on this, and I think I did a poor job since I am writing this on my phone instead of my computer.