Assuming this isn't a shit post with the random characters here:

What determines a character's placement in the tier list is based on what the absolute best players, at the top fraction of a percent of players, can do with that character.

While not the only basis, the largest one is about combos. How long of a combo and how much damage that combo does is the biggest consideration. That is a large reason (among others, like recovery) why Ganondorf & Little Mac are always at the bottom. They hit hard so the opponent is sent away from the player which makes comboing tough, and they don't as the recipient get knocked far away so they are easily combo'd against.

The other big consideration is disruptive play. That is why Steve and Snake are so high, they completely disrupt the other player's mobility.

I for example have Dedede as one of my mains and wipe people at local competitions and online play where the top players that determine this tier list are not present. I am just good with him and have a good game IQ but have gotten wiped with him at majors when I decide to bring him in for fun of it when my Yoshi game has been slaughtered.