I think it's just the terminology which may confuse, as essentially anyone saying they 'grade on performance' is really saying they don't grade at all, as all bats will perform regardless of the look of the willow.
I don't have an issue either way. The buyer will make their decision and if dealing with a reputable company/person will get a bat which performs. It just might be they pay more than they would elsewhere for the same grade of willow.
However I don't think anyone is being underhand. Grading can be confusing for a lot of people, even those who play the game, so in some ways this may actually help?