I suppose I've approached it this way before also,lol,tintin seems real curious about this very subject,that is I notice he several times he post things concerning the issue of Gen.6,me also(my curious nature) which is why I try to read along when someone begins a thread about it. So it makes me wonder "whats the pay off?" I mean would it change the way we would look at other things in scripture if we knew the answer thats why I ask about how we would see the man of sin in the end.
In the letters of Paul he explains that there are mysteries that were kept secret from the beginning some were revealed(Christ in you,Mystery of the kingdom of God ect.),although at the same time there is still the things sealed(kept a mystery) at the end of Danial,mercy seat(we cannot yet speak,ect.), mystery Babylon ect.ect.
I think it's wise to see things scriptural "captive"(comparing whats written with other scriptures,as we are),but at the same time how do we determine "captive from non-captive in scripture"? One will say only the books in the KJV,another will say "well,1 Enoch,apostolic fathers also" others will include A.H. from Irenaeus,and other books still in their definition of "captive books" to see as information to include.
As we know Irenaeus was a hearer of Polycarp,Polycarp a disciple of John. So trying to understand what Irenaeus believed/thought about this subject (to me) is important because he lived so close to the time Rev. was written so there was less percentage of error(less than us 2000 years later). Irenaeus wrote A.H. about ad150-170 so less than 100 years after approx.date of Rev.(ad96). So in the same aspect if this is 2015 then me and you would be able to discuss things that took place in 1915-1925 with a fair degree of accuracy. Even still there are people who are very old but also born in the 1920"s(or their family members) that would have been told about the events during their lives.
Genesis 6 I think is a puzzle,lol,,,as you say all we have to go by today is what we have in the scripture(I agree),,,looking into this from another angle though I'll tell you something I noticed working on my math problem "not only does Irenaeus discuss the things valentinus,potolamaos ect. were doing (incorrect) in A.H. he also is stating the correct manner of approaching it",,,so there in is also a "list of the correct steps to take to reason it" he learned from Polycarp,who learned it from John,but it's a "mystery" which it was not spoken at that time
CHURCH FATHERS: Against Heresies, V.30 (St. Irenaeus)