The WN9 rating was launched summer 2016 and aimed to be simpler and better than WN8, but it never became popular. The ones behind it has not added expected values for new tanks, and not rebalanced the values for existing tanks as they have been nerfed or buffed.
The first rating was the EFF rating, then came the WN-ratings. Wot Numbers now support both EFF, WN7, WN8 and WN9. Calculating all these ratings takes some capacity, so removing some of them would speed up the system a bit and make it easyer to maintain the system.
Please leave a comment below: should we remove some of the non-relevant ratings?
Would be nice to get some feedback about it