For me I would prioritise the quality of the copy. Its the copy that will build trust, create a great user experience and persuade users, and so actually SELL the product.
The on-page grader with MOZ is great but don't be obsessed by it. Measure what you do in terms of sales, not whether you get a B or an A+ on the grader.
Finally, you can see how intelligent Google is getting at understanding and processing synonyms and meaning in different contexts. As good as the MOZ grader is, I don't believe it can operate at that same level. The good news about Google's intelligence is that it can free you from slavishly forcing keywords into your copy.
Hope that helps!
