I think you really underrate Knight, like extremely so. He only had 2 points fewer than Granlund, he may have had more games played, but he never had set linemates (where Granlund was almost exclusively with Reinhart) and never received first line minutes (3rd line more often than not). Knight is also bigger and more physical, better defensively, better on draws and from what I saw more of a leader.
And they aren't just going by "safe picks", they just think the difference between 6.5 and 7 is overcome by him being more likely to achieve his potential. They also have Janko with higher end potential than Granlund (which I agree with 100%) and the same odds of reaching their potential (which I also agree with).
The way I look at HF ranking is like this. I automatically subtract points for the letter. Since 7c means it could drop 2 rankings, so I just subtract the 2. So I see Granlund as a 5 and Knight as a 5.5. So since Janko is a 7.5c, I see him as a 5.5 too, but since B>c, that is why they have Knight ahead of Janko. But is Janko was an 8c, then he would slip ahead of Knight. I don't necessarily agree with their rankings, but that is how I break them down to understand. In the end they are all extremely close and no one is right or wrong.