Was it ever "canon" per say? I thought it was always just a good insight into the author's mind, so we know what knowledge base the films were built upon, but could freely be contradicted if need be. Same with Lucas' statements.
Disney has just been changing a select few things. Doesn't mean every intention behind the films has been retconned. I imagine Dooku is still an 8, Windu is still bordering on 9, Yoda and Palpatine are both still 9's. I don't know if Obi-Wan is still a 7, considering his story's been elaborated on a bunch more than of the above.
Personally, I think it's one of those concepts that would need to be directly referenced for it to be considered canon. Gillard's system has the gap between the various numerical designations as massive, iirc. Like, an 8 would be worlds beyond a 7 and so on.
Granted, there's still a discrepancy in skill between Anakin, Yoda, Mace, Palpatine, Dooku, Kenobi, etc., but in canon at least, we don't know how significant that gap really was. We just know that there was definitely a noticeable difference between them.