Top Tier is NOT about how much detergent and additives are added to the fuel it is about the types of detergents and additives used that prevent carbon buildup, valve sticking; injector and engine cleaning specs. It also guarantees that no metallic type additives will be used. A good example is ferrocene (iron) and methyl cyclopenta dienyl manganese tricarbonyl (MMT) use to replace lead can lead to spark plug fouling and early catalyst damage, and top tier prevents their use.
You can add ten times the amount of a detergent to a fuel but if that detergent is not effective, it will not do the job. Does Marathon do the job? NO way of knowing since I am not privy to their testing info, and I guess they don't want to pay for the independent tests and fees required for a Top Tier designation. That DOES NOT mean Marathon is not good fuel. I used it when living in MI since it was a predominate fuel in that state and never had a problem. But back then I kept my vehicles no longer than two years, so I really didn't care. I have read that BP, which is not a Top Tier, actually passed the independent top tier test but did not want to pay the fee to the top tier organization, which is not just GM it is also BMW, Toyota, Honda, VW and Audi (I believe that is all).
Here in Moab, I use Maverick quite a bit on the H3, but about every other fill up I use Chevron. So far the new truck has used either Chevron or Conoco.