I review myself based on ilvl. If I go by overall, I am gonna get a whole lot of people up against me that are way ahead of me on gear, and that will give me no indication whether I am on the right track or not.
I am talking dps ranking btw.
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That's assuming no skilled players stay below mythic raiding, which is not true. You will however have a better pool of players to compete against on mythic content.
Personally I don't use the ranks as an indication of how good I am, I use them as a indication of being on the right track or not. My higherst dps character is 940, and I've been parsing really well on her by ilvl since ilvl 915(several orange parses, and 2-3 100% ones). Curious as to what was going on here, we looked a bit more into it, because I actually didn't understand what I was doing right. I am still not sure how I do it, but the spec flows really well with me. I am not gonna be able to go much up in ilvl on her sadly, but I ejoyed following my ilvl based parses through ilvl increases.
However, going on to another alt I parsed blue quality logs, and going by that I need to check up how to improve that. Had the same with an alt before that too, the ilvl ranking told me "something's off. Locate and fix".
So yeah, even at normal/heroic level those rankings are a good indicator. Doesn't mean you are the best player in the world, but it tells you which direction you are heading.