Please note that it is Esau the person that Paul is speaking of, not Edom, his descent.
Hebrews is 100% about individuals, and their personal spiritual state. He notes that Esau tried tearfully to repent of his error. Esau had the same spiritual upbringing as his brother, but a far different final outcome.
Of course it was but with Esau selling his inheritance his entire progeny was affected. But your initial comment that I responded to was "backsliding". Backsliding does not equate to "selling ones inheritance". In other words completely and irrevocably putting this worlds wants or needs ahead of our eternal inheritance.
Here is the key phrase "Thus Esau despised his birthright". Esau didn't just "backslide" from a commitment to his inheritance. He outright rejected it for a momentary need. To equate Esau selling his birthright to simple backsliding presents the wrong picture I believe.