I don't think that the interpretation of Genesis 6:1-4 is too difficult if you look at the context.
I suggest that the 'sons' of God are the male line of Seth, and the 'daughters of men' are the female line of Cain. There was inter-marrying between the two families with the result that the knowledge of God and His righteous laws was lost.
Or more prosaically, 'Take heed to yourself, lest you make a covenant with the inhabitants of the land where you are going, lest it be a snare in your midst......and you take of [their] daughters for your sons.........' (Exodus 34:12, 16).
And
'Do not be unequally yoked together with unbelievers................etc.' (2 Corinthians 6:14-18).
It is surely the simplest and most obvious one.
This scripture does not lend itself to an Occam's Razor style of interpretation for open debate. I'm just going to point you back to the book and just say that the Sethite view has always had scriptural problems... (because it was never the correct interpretation mainly)
Heiser's work for all intents puts a fork in the Sethite view... there's just no historical backup for it.... It's mostly based on wishful thinking and a denial of the Supernatural background of the events of Genesis 6. That's why he produced a laymen's version:
Your Exodus 34 reference actually supports Heiser's work through his highlight of Deuteronomy 32:8-9 (ESV) as a more proper World-view of Scripture.
Contextually... the 2nd Corinthians reference does not fit properly for your argument... but since its the only New Testament reference that someone with a Sethite view can use to cram a square peg into a round hole... I understand why you've deployed it.
Thanks though.
BB