haha what
The tiers are at least slightly credible. They are based on which characters win the most tournaments, and therefore they are based on the preferences of players who win a lot of games. While it is based solely on opinion, it does hold
some meaning when it comes to choosing your best character. It just shouldn't decide for you. There are no "best" or "worst" characters. Just characters that some people like more.
Regardless of that though, you should try all the characters and see which one matches your play style the best. Everyone plays differently and should have different characters to suit them.
Maybe the platforms change positions every now and then
No that's the battlefield. It's the classic smash bros map. A large platform with three small ones. Simple as that. It was just edited for video reasons. Check out the beginning of the video when the platforms are all still there.