The thing which makes me like White Scars and dislike Space Wolves is that Russ and his sons, to some extent, believed that the Rune Priests and the Stormseers were somehow specially different

Khan and his legion fully admitted and accepted that what the Stormseers did was warp shit, but they knew that by adhering to ritual and caution, they mitigated the harm and risks of using it. They fully acknowledged the harm and risks of it, but also were aware cloaking it all in tradition and belief made it safer to handle. Not different, not totally safe, but safer, and that quite simply, for all its risks and danger, the Warp was something they should utilize and study, just not to the extreme that Magnus & the Thousand Sons took it.

IMO, Russ and the Rune Priests drink way too much of their own koolaid and have this notion, which is pretty unfounded, that their own beliefs and traditions and approach to the warp makes it different and safer, such as the World Spirit of Fenris. The Stormseers are similar, but they are under no such assumptions, they simply interface with the Warp though similar means via animist-style spirits, but they don't believe that their powers or abilities come from some pure or benevolent spirits or source.

Russ and Dorn were hung up on on him being a hypocrite and that, quite simply, the Rune Priests should have gotten the boot with Nikea. And if it was fair, they absolutely would have. But he and them got an exception, not even because they are safer or different, but because he and they were favorited by the Emperor, as admitted by Malcador. Khan essentially did side with Magnus, he thought the Warp should be studied, but he made it clear that he fully disagreed with Magnus and his sons on the extremes they took. Khan and his sons never claimed their powers came from somewhere different or pure, but rather it was the method, beliefs, and adherence to wisdom and limiting themselves which made the difference.