Obscure readings not withstanding - The idea that these proven and accurate translations are just 'too difficult to read' on even that obscure text - is very difficult to prove and thus no argument is possible from Genesis 27 - against Christ's "Sola Scriptura" method of Mark 7:6-13 or the NT saints doing that same thing in Acts 17:11.
Genesis 27:39-40New American Standard Bible (NASB)
39 Then Isaac his father answered and said to him,
“Behold, away from the fertility of the earth shall be your dwelling,
And away from the dew of heaven from above.
40 “By your sword you shall live,
And your brother you shall serve;
But it shall come about when you become restless,
That you will break his yoke from your neck.”
Genesis 27:39-40New King James Version (NKJV)
39 Then Isaac his father answered and said to him:
“Behold, your dwelling shall be of the fatness of the earth,
And of the dew of heaven from above.
40 By your sword you shall live,
And you shall serve your brother;
And it shall come to pass, when you become restless,
That you shall break his yoke from your neck.”
Genesis 27:39-40Young's Literal Translation (YLT)
39 And Isaac his father answereth and saith unto him, `Lo, of the fatness of the earth is thy dwelling, and of the dew of the heavens from above;
40 and by thy sword dost thou live, and thy brother dost thou serve; and it hath come to pass when thou rulest, that thou hast broken his yoke from off thy neck.'
Genesis 27:39-40King James Version (KJV)
39 And Isaac his father answered and said unto him, Behold, thy dwelling shall be the fatness of the earth, and of the dew of heaven from above;
40 And by thy sword shalt thou live, and shalt serve thy brother; and it shall come to pass when thou shalt have the dominion, that thou shalt break his yoke from off thy neck.
I am not sure why you think Genesis 27 is an "obscure text."
But if you read carefully - both versions (that he was blessed and that he was cursed) appear in the 4 versions you quote.
All of them agree on "thou shalt break his yoke from off thy neck."
All of them state that Esau lives by the sword. The fact that NKJV/KJV/NASB compared sometimes yield more accuracy one way vs the other - is like noticing that at some times NASB leaves out a verse. Old story - not sufficient to dismiss the Bible teaching on sola scriptura testing that they all report in Mark 7:6-13.
hence
Gal 1:6-9 "
though we (Apostles) or an Angel from heaven should bring to you any other (opposing) doctrine - let him be accursed" -- "sola scriptura" testing is what enables us to follow Paul's teaching in Gal 1