These tiers were tested in Time Trial to see who exactly are the best/fastest characters. The same rules applies for Multiplayer online as well IF you're in a lobby full of really good players and if they can dodge and evade all of the chaos that goes on. Though, depending on the situation and all of the chaos, any character has a chance at winning.
I think, for multiplayer, there is no BEST character. The mods are in the game exactly to balance everyone out.
You're partly right. I think how you can rank them is on annoyingness in battle. They are always so much ahead of me when playing Ralph, Pudding, Joe Musashi, AiAi and Ulala then score, at least for me, top place However, I've played this game for more than 20 hours, but MeeMee, Knuckles, Shadow, B.D. Joe and Vyse had not won at least 4 times, Unless I play with them.