i think we arent considering that a move might be extremely good, but cannot be used optimally due to a certain characters mobility
for example, ganon's dair would be ten times better if he had wario's air mobility for the simple fact that it would be easier to hit, and more applicable as a punish move
also, if mk had more mobility in the air, his aerials would also be better even though they're technically the same
same thing, if wario had luigi's air mobility, his aerials would be useless
however, if we judge moves based on how the character can apply it, then i think mk's SL is the best move in the game. it gives a constant threat above him even if you are out of range for any aerial, but if you try to airdoge the SL he can just uair you afterwards, its also too quick to airdodge on reaction, which makes it really got because it hits so high (ow, and i suppose you can punish the airdodge with the glide attack?) screw meta knight...