I don't get why people think that L-cancels are extraneous. In basketball, if you foul someone who makes a shot, not only does he get the basket, and a free throw, but the other player is also issued a foul. Why not just give them 1 point and not have them shoot the free throw? Or why give the free throw or point if they made the shot? They are triple punished, as the foul penalty is enough in itself. In basketball, the free throw is there because hell, at the end of the game you can't just give him the points, its a physical sport and he has to be able to make the shot. It's not just a game of strategy, it has a performance element to it as well. If someone messes up something that is routine, it can still become a turnover that could cost them the game etc. L-cancelling exists as a routine performance element that when messed up provides an opportunity for vulnerability that isn't there simply from reducing the landing lag of all aerials by half...
and guess when most people most often make mistakes? ITS WHEN THEY ARE UNDER PRESSURE. It's an opportunity that could earn you a stock or cost you one. So it's not as if it doesn't hold sway in a match. Its the whole gaming element, hand-eye coordination, physical performance, mental performance, and endurance. This isn't just a game of chess where your physical ability to perform a move under pressure doesn't come into play, where its mainly an issue of mental performance and stamina. Just like competetive sports, a physical aspect helps make the game even better because it's not just about whether you're smart enough, but also whether you can go out there and execute your strategies... and that in my opinion is what makes this game so great.