
Should not be in D, it has just 10 frames of endlag and does not send the victim very far. It's biggest issue is that it's a horizontal combo throw and Falco's movement stats are awful. DI away keeps you safe past 50 or so on most of the cast. As well as keeping you safe from aerial followups in general. Before that, there's Dthrow to Usmash and Dash attack if Falco knows your DI is consistently away. I'd say C because it's ruined by good players.
Or its knockback since it will start sending people out far... And the 50 degree launch angle since it's going to be easily DI-able. Then again, we don't want a Robin D-throw on Falco considering the absurdity of it. If only it was a 50/50 style throw, but not as crazy as Melee's.
DI it, tech it, or if you have access, use a fast aerial or fast and/or armored/invincible Special to stop any followups from Falco even during low percents since Falco has to run after you no matter what percent D-throw is used at.
He's really only going to get dash attack, Nair, Fair, or Bair and of those options, dash attack can be avoided by teching, Nair is the most damaging because he can chain into them, but it's short-ranged and Falco need to jump which means he's going to be in the air with his slow air speed, Fair's startup plus his 6 frame jump and DI can make it very unsafe, Bair is actually unsafe against some characters at low percents due to it having no base knockback, so he needs to land to deal with its lower landing lag or auto-cancel compared to its normal recovery. Up Smash works better on fast-fallers, but it's committal since if Falco Up Smashes, he's not going anywhere; reverse jump-canceled Up Smash will have slide further, but at that point, you might as well just Bair.
At mid- to high-percents, none of those options work unless you let them happen. One option, however, that can work reliably is aerial Blaster. At most, 2 lasers which is 6% unstaled, but still something. D-throw is the only real set-up for Blaster. Not as great as if they were possible, D-throw to Charge Shot, D-throw to Sun Salutation, or even D-throw to Hadouken and Shakunetsu, but it's still something for Falco to pressure from afar. Only really works since aerial Blaster is frame 9 on startup, lasers still travel moderately quick, and aerial Blaster's rate of fire is faster (by 7 frames per shot), but of course, the risk of this is aerial Blaster's 41 frame recovery which doesn't really matter at that far of a range and its low set knockback which is why Blaster should never be used at low percents or even mid-percents from D-throw.
Fox's D-throw is kind of similar to Falco's; similar problem of DI, teching, and options stuffing out Fox's, its angle and knockback, but also higher recovery at 21 frames. Fox can do similar things, but he doesn't have Falco's Nair to chain Nairs and Fox can probably use Blaster to followup at mid- to high percents, but without any knockback, and compared to just running up and pressuring, it's not as "useful". Falco makes use of his 10 recovery D-throw for low percent set-ups, but because of his low horizontal mobility combined with D-throw itself, he can't get much out of it past that; Fox makes use of his raw speed for his D-throw set-ups, but because of D-throw itself, especially the higher recovery, he can't get much of it past low-percents.
Between the 2, Falco's low percent set-ups are more "guaranteed", but in the long-run, it's the weaker throw in terms of damage and Falco's ability to do anything significant since he's too slow to run up and pressure after it. Fox's low-percent set-ups are shakier because of the higher recovery, but in the long-run, it's the stronger throw in damage and Fox's raw ground speed can still allow him to pressure with it. Falco and Fox are much more dependent on their U-throw for set-ups which has similar differences; Falco's set-ups are more guaranteed and U-throw is a stock cap, but as Falco's overall aerials (and moves in general) are weaker in KO power than Fox's, especially vertically, it's not as threatening; Fox's is more devastating considering his much stronger Uair, but Fox's won't realistically KO and it's a set-up not being able to combo at any percent. Anyway, I digress.
They're pretty shaky throws; low-percent niche throws like their F-throws. I think they're fine where they are at D-tier. Yes, Falco can use it for low-percent set-ups, yes, Falco's Nair chains can rack up a lot of damage, but that's it. After that, D-throw is pretty much pointless like F-throw and B-throw are for both Falco and Fox. All you get is positioning which for Falco is at most 7% with F-throw to 4% at worse with U-throw where he can at least set-up with. The others are 6% B-throw whiffed laser and 5% D-throw. Fox on the other hand has to choose between 2 7% throws, F- and D-throw, and 2 at worst, 2% throws, U- and B-throw missing all the laser followups. Where the hell did you learn to shoot, Fox? The Stormtrooper Academy? Yeah, that 2% U-throw is looking mighty fine when Fox knows if he lands a Uair, you're dead. They don't do a lot of damage, positioning is at best, average between their other throws and bad compared to other characters with more damaging D-throws, and their set-ups aren't that rewarding. Fox can run up and Bair you, but that's it since Bair is going to send you flying while Nair isn't going to do much, Uair and Fair are risky when used that low, and Dair isn't a horizontal move. U-throw lead to Uair juggles which is devastating not to mention Fox's ability to trap landings.
I'm with Falco staying at D-tier or if he moves up, Fox's to C-tier as well. Falco's low percent follow-up edge isn't really enough in my opinion as Fox can just do the same things, but through his raw speed to make up for the higher recovery. Similar, not so good D-throws with similar problems.