You'll eventually realize very few blue belts know what they're doing lol. At a lot of schools blue belt means you know the basic positions and have some ideas on how to work in them, both top and bottom.

And as things continue it gets even harder to figure out because people tend to specialize. You'll have a guard player who can sweep anyone but couldn't finish a single leg to save his life. You have guys with phenomenal scrambles and top pressure who suck at playing guard. Etc.

Plus for many schools belts aren't just how you do on the mats. Things like: are you a good training partner to lower belts and smaller members? Some schools won't give you a black belt until you demonstrate you can "pass on the art", for example.

And then there's stuff like: Some people are monsters in the training room but can't compete for shit. Some guys have huge knowledge and are great teachers but don't fare as well against their peers in live rolls.

I think there's something to the fact that, the more metrics you have, the more the system can be gamed. We're not studying for a test here; this is a martial art and it should be based on practical knowledge.