Problem is it doesn't work logically, or at least within the realm of what a tier list is.Okay, so, the following...
The tournament placings are taken into account, but not to such an immense amount that it would matter that much.
If players regularly place with Samus, that would, at max, give her 2 or 3 spots higher. Problem is, though, due to the fact that Samus isn't as good as MK or Snake, and doesn't have as many players placing with her like with them, in the end, it wouldn't matter that much.
What I want to say: You can be the very best player in the world placing regularly first with Samus in all kinds of tournaments... it wouldn't make her a better character.
If the best playing in the world uses Samus and wins with Samus, it means that he/she is doing something right with the character. If someone is winning tournaments left and right with a characters that is considered bad then something has been overlooked. Said player would be using techniques and strategies with the character to allow him/her to be victorious, meaning the character would be high enough to allow him/her to win. If characters are a limiting factor, and someone is winning, then the character is better then expected. It just can not work where the character is bad, but the player is winning everything with that character.
The two have to go hand in hand. If something like that happens, then the tier list is wrong.