It probably would be logical to think of "skill" and "victory" to be synonymous, but I definitely agree that they truly aren't. Especially since the difference between the two was illustrated by the hypothetical example of MK and Link both placing second in the same tournament in two congruent instances. The overall consensus would be that the Link was the more skillful player because he was a lower tier. Despite this, we would have no idea how the Link would do if he went up against the MK; however, if he loses, it would be a perfect example of the difference between "skill" and "victory."
To answer Sleek's question, I could not name a specific tier, but it does appear to be agreed that the lower tiers are often the most hard working tiers. It was once said that "hard work beats talent when talent doesn't work hard." If we consider talent to be placement on the tier list, then it explains why some tiers do worse than the bottom. Though those tiers are technically more "talented" than the bottom tiers, they do not do as well because they feel comfortable at their level and are therefore more lazy. Of course, this is not always true, but it might serve as an explanation for Sleek's point.
Finally, to answer the initial question, it truly depends on the player not the charater being played. With your examples of Blubba & Deva, San, Rebaz, and RayKalm being able to fight amazingly well for their given main, I would say that they are good (using the trend that more positive is the same a more skillful), if not amazing, players. However, to say that a person maining a lower tier is automatically better than M2K would be false. Nevertheless, it is purely dependent on the player of the game, because it is the player who controls the character, not the character being played.