Late reply, Falco's Dtilt doesn't have subpar range. It's noticeably disjointed after his tail's tip. Falco's Dtilt has about the same or even slightly more range than his Ftilt which itself has good range for a melee move.
First, to clarify some things, Falco's Dtilt is both a disjoint and is disjointed. Since he uses his tail to slash people, the move itself is a disjoint as his tail isn't considered a hitbox; it's basically like Ike's Dtilt or any of Ike's moves where he uses Ragnell. At the same time, it's disjointed from the tail's tip. Where his tail ends and where the attack trail is shown is not its maximum range. Its real range, is about a third more than what is shown. Inversely, Fox's Dtilt's range isn't where his tail tip is or the attack trail, but before it. Fox's Dtilt is a disjoint, but not disjointed. Basically, the game lies to you about Falco and Fox's Dtilt range. Much worse on Falco since you can't even see the hitbox and bad, but not as bad for Fox since while he's missing range, it's not a massive blind-spot since it's only his tail tip, the white furred part of his tail.
From the listed posted, Fox and Luigi should go down, especially Luigi. First off, I'm not a Fox or Luigi expert, so I won't be entirely knowledgeable on them. Luigi's Dtilt is this weird, very short-ranged -- I think it has the shortest range of all Dtilts -- Dtilt that doesn't seem to do anything. It used to have a high, vertical hit angle that Luigi could use to follow up with aerials, but 1.1.0 changed it to a 361 angle making it more horizontal and made it easier to trip with since he isn't popping people up, however, it can't set up as well... I remember someone saying the angle change was a nerf. Either way, Luigi's Dtilt remains situational. It's pretty much this weird move that exists to be weird because Luigi was made to be weird. At the same time, this makes it pretty much a joke move. Luigi's Dtilt could probably end up as a D- or F-tier Dtilt.
Anyway, some other stuff. Ness and Ryu are the only characters with Dtilts that can be repeated. I don't mean like low recovery, I can continuously Dtilt like Diddy or DK's Dtilts, but there's a property? that makes it so Ness and Ryu have lower recovery if they choose to Dtilt again. For Ness, Dtilting again has 5 total frames instead of 13, so the recovery drops from 10 frames to 2 frames. For Ryu, light Dtilting again only has 6 total frames instead of 14, so its recovery drops from 12 to 4. A similar thing exists for jabs where if you hold down attack, some characters will repeatedly jab in place like Capt., (Dr.) Mario, and Fox while others like Cloud and Lucas apparently have lower recovery if they choose to jab 2 to jab 1. Also, Ryu's light Utilt has this property as well. Anyway, keeping that in mind, Ness's Dtilt while not having a lot or range or power, has a lot of speed. It's really a cr.LK like in a traditional 2D fighting game. At worst, probably a C-tier Dtilt and not a D-tier Dtilt.
Links: Ness's frame data:
https://docs.google.com/spreadsheet...9tivelrRJvPl7o1dBhgYo/edit?pref=2&pli=1#gid=0.
Ryu's frame data:
https://docs.google.com/spreadsheet...GinKOYVI3RnpS43ERGvJM/edit?pref=2&pli=1#gid=0.
Also, isn't Jigglypuff's Dtilt basically a slower, but stronger Kirby Dtilt? Part of me wants to vouch for Jiggles and PAC-MAN's Dtilt, but I can't explain why.