If you think a little further you'll realize that any precision between 1 in 6 and 1 in 5 or 1 in 7 would be pointless, so your argument is complete nonsense.
This guy has every right to shout his opinion into the void. That's the double-edged blade of Twitter. But trying to claim your opinion is objective fact by saying "it's science" like Ron Burgundy makes him look awfully dishonest.
I know that's what he's doing because you can't bullshit a bullshitter. I used to do this same nonsense when I was in middle school and I thought I was smarter than everyone else. But I grew up.
Your claim that Tegmark is treating this as fact is not supported by the evidence I see in his lesswrong article (note: not a scientific publication) where he is asking others which percentages in his model they disagree with; that is not the behavior of someone claiming his assumptions/conclusions are a fact.
You yourself are being sloppy with the truth. The numbers on the graph are made up? Agreed. Out of thin air? No, RTFA. Non-authoritative? Agreed. Tegmark is presenting his opinion as scientific fact? What are you smoking? Quit projecting your teenage self onto Tegmark.