I work on the Product team at Moz, and really appreciate this feedback! It's important to us to improve your experiences using our tools. The On-Page Optimization tool is best for identifying low hanging fruit. Say you're showing up on page 2 in Google for a keyword you really care about, and your On-Page Grade for that keyword is a D. Optimizing your page with On-Page report suggestions may just give you that push to page 1. That said, if you're already ranking #3 and receiving a B grade, bumping it up to an A+ might not be the best use of your time. We're working on ways to visualize the sweet spot of opportunities in future versions of Moz Analytics.
