The majority of low tier's either have poor recovery and/or poor speed. Snake, Wario, and DDD are the exception, just because their recoveries are good for heavy characters. The majority of high and top tiers are filled with the faster characters. Fast as in, quick attacks with little start up time, or quick attacks with a quick cooldown time, or fast as in running speed, or walking speed, and aerial speed. Any aspect of the what I mentioned, is what makes a character have a lot of potential. Having a lot of power with nothing else, is bad. Just look at Ganondorf. Speed is one of the most important aspects in a fighting game. That's another reason why Kirby will be going down the next tier list, Kirby is too slow to avoid projectiles and catch up to speedy spammers. If Kirby was as fast as MK on the ground, he'd be in A tier for sure.