Yes, there are several grading systems. We don't use them. However, when I have to re-read a simple sentence or paragraph 4-5 times, and perharps read the whole text or even search about a product in order to understand what they are trying to say, then it's a pretty clear indication the text is muddy!
Yeah, I think a pretty good job can be done with sppropriate criteria. This is essentially what grading systems try to achieve - I think the IB program has wrestled a lot with this idea.