Sorry to have revived this thread.
Mario's DTilt may be a bad move, but it isn't the worst. It's probably on par with Ganon's DSmash as the worst. Let's compare the two.
Ganon's DSmash hits at frame 16, has 20 frames of lag after the first kick, and 27 frames of lag after the second. So, overall, it has about 47 frames of lag. It does 5% damage with the first kick, and 14% damage with the second kick.
Mario's DTilt starts at frame 7, I'm not sure when it finishes (but I'm positive it ends waay before 47 frames of lag). It does 5% damage unsweetspotted, and another 2% onto that if sweetspotted.
Ganon's DSmash has alot more range, and power, but it DOES NOT kill. Unless you want to consider 185% a kill percentage.
Right now, Ganon's DSmash does infact look better, it does more damage overall, and has more range. Though, that could all change, just cause of one major flaw in the move. The second hit is airdodgable. Ganon's DSmash turns into a crappy move like Mario's DTilt, but worse, just because the second hit is airdodgable.
Both moves do 5%, however Ganon's move comes out 9 frames slower, both moves put the character using it in a bad place (considering a airdodge is done after the first kick of Ganon's DSmash).
The only difference now is that Ganon's Dsmash is slower, and has more lag to punish. Mario's DTilt has less range.