I suppose I wasn't talking about just the Mythic score, rather the entire 'checking wowprogress' thing. Being able to check what keys a player has done is extremely useful and the score reflects that. If someone has done a lot of +15's they'll have a score that will indicate to me that they're worth taking to a 15 or 16. I don't just look at the score though, I scroll down to see what they've done.
I'm new to the wowprogress thing myself, though. I've been trying to get my score up precisely because I find it useful myself to check when I'm the one forming groups. Currently my score is 1.8k but I've not done upper kara yet, at all, and so I expect it'd jump to 1.9 when that's done. WoWProgress shows others that I've done most dungeons on 15, some on 14 and some on 16.
Maybe I'm thinking of something else and we're not talking about the same Mythic score as I'm not sure what you mean by the score is completely random. The column on the right 'score' seems pretty solid to me. The higher key you do, the higher the score and presumably, though I'm honestly not sure, that score is increased a little by how fast the key is cleared. A 14 gets me a score 140+, a 15 gets me a score of +150, a 16, 160 etc.
https://www.wowprogress.com/characte...crest/Sarithus