I don't understand what's with the sudden obsession over 'grading' people's performance in grouping content. There already are tools out there for those who wish work on their performance: Online guides (in both written and video form), DPS trackers, Parsers, etc. I don't see a need for an integrated grading system (not to mention these things are never accurate and fail to factor everything in such as mechanics and other people's actions).

What if you're doing your job perfectly, but the healer is struggling and you end up dying? That's gonna lower your score even though the fault isn't yours. What about mechanics that force you to move and thus it either lowers or interrupts your DPS entirely? The grading system won't take that into consideration either. Top players would most likely know how to read into the data, as is already the case, but the proposed system is more aimed towards casuals who would get little to nothing from these arbitrary grades beyond feeling bad for themselves for not getting a good score.

Grading at the end of group content won't suddenly motivate people into perfecting themselves, whacking away at target dummies for hours on end. The normal content isn't hard enough to justify that kind of effort either.