1,700 (what the research paper estimated) and 2,000 (what one researcher seems to have rounded to) is a big difference, historically. 2,000 years ago, Jesus was still a minor. 1,700 years ago, the gospels, interpreting prophecies from a significantly different version of the bible, had swept the Roman world.
My bet is that the handwriting analysis is valid (c. 2nd century), and the scroll dates to some time shortly after the destruction of the 2nd temple; the fire messes radiocarbon data up.
You think the Septuagint is a "significantly different version of the Bible"? I thought it is simply a Greek translation of the Hebrew OT with some literary adjustments made for Greek idioms etc.