Neb
Smash Lord
G&W's utilt is gay and shouldn't even be compared to MK's, its just handy for quick combo's at early percentages. Like you said, some of the moves serve different purposes, you just can't judge one from the other. GaW's dtilt is used as a spacer (So decaying isn't the focus of the move), MK's used for damage racking. But yes, it is pretty quick, has zero cool down.5 frames is a whole lot of frames. A lot can happen in 5 frames. Extremely evasive characters can block that so much more often than MK's downsmash.
In practical play, G&W gets a lot of low% kills with his downsmash because it's a "sleeper" move, people aren't used to the huge range.
I think MK's uptilt reaches up higher than G&W's... but i'm not going to argue that MK's is better. The two serve different purposes, and really MK's uptilt gets press because he doesn't have as many kill moves as he would like.
Like Emblem Lord says, only G&W's lid is really really fast on the ground. I can't deny the move is wicked awesome, but it decays after a while. Meta Knight's ground moves combo more and rack faster. MK's downtilt might not have the lid's range, but it has a greater payoff and is equally fast.
MK can already be doing another move because he's done with the smash, he doesn't need IASA frames.
And while MK combo's better, G&W's does better damage. MK can go around comboing for a measly 15-25%, while Game & Watch can throw out two bairs/nairs/fairs, or one dsmash/usmash/fsmash and get the same result, better in most cases.