I'm not a big fan of the rating scales that we have. They give a general idea as to the purpose of the tire, but as you state, when the rating is 1-5, you're going to get some instances where the ratings don't reconcile. As for the Marathon vs. the Marathon Plus, the difference in the rating scale is that the Marathon is 5 gray boxes, the Plus is 5 Blue boxes. Blue denotes (in our case) the highest possible ranking. This last subtle difference is not always apparent as one is flipping back and forth between pages. A rating scale of 1-100 would work better, but wouldn't fit neatly into a catalog or on a webpage. In Schwalbe's case (and likely in Michelin and Conti) I do believe that the information provided is useful (when combined with other sources of information).

I think one has to look do their research if they are looking for the "perfect" tire. My own opinion is that the "perfect" tire doesn't exist, at least not in reality. There are always trade-offs. If you want the best puncture protection, you're going to compromise on road feel and grip. If you want a tire with the best possible road feel and grip, it's not going to provide much puncture protection, and it's going to wear out relatively quickly.

With regard to "marketing", I think most of the name brand tire manufacturers do a pretty good job of making a quality tire, and describing how the tires are made and what their purpose is in their literature. In the end, the proof really comes down to what the consumers say about a product; marketing can't change what actually happens in the real world.