Every single one of Metaknights special moves leave him unable to attack again if he ends up in the air with it, with a minor exception with his up+b. That's probably the biggest reason why they play a lot differently. Also, Pit's light arrows are very quick and useful, so, again, that makes a major difference.
Metaknight's neutral A results in continuous attack, where Pit does not, but aside from that, Metaknights slashes are much quicker than Pit's.