Bagmarks are important, but I agree that they aren't the only thing to focus on when grading. I do have an issue with some super baggy Morgan grading 65 or higher (I do believe gems should be relatively less baggy). I also believe that my two examples above were given 65s vs the 1891 being a 63 in large part based on market grading. An 86-P or 80-S in 65 is worth about the same as an 1891 in 63 on the market. And if the 1891 was a 65 with a greysheet of $1,700, I'm confident that I would not have been able to win the coin (as it would have almost certainly sold for above that price in a higher end auction).
If it were a 65, that coin would have gone for $5,000 plus in an auction of serious toned coin collectors. When one gets into the 1891-1896 ballpark, we are talking about good-better-best date Morgans. It was undoubtedly market graded to keep the price under the gem level. I also agree that toning and surface preservation criteria are very different for the 3 mints (not considering Denver, as all we have is the 1921 D). Philadelphia coins do not tone as vividly, for the most part, as the storage was much drier than New Orleans or San Francisco. Most of the vivid textile toned rainbow coins are “o” mint, as the storage was damp, humid, and haphazard. Philadelphia coins in general have better strikes, although not as strong as the 1879-1889 S mint Morgans. So, there are many variables.