While scrafty seems to work well in theory, in practice it's actually very disappointing. It is neutral to basically all priority and weak to mach punch / vacuum wave, so it's easy to pick it off. Even at +1, as you said, a ton of stuff outspeeds it even unboosted. Way more than you mentioned in fact--starmie, base 120s such as alakazam, weavile and stuff. And basically EVERY scarfer--including, as you said, scarfkion, but also scarfdeo, mence, chomp, even scarftoed. It has low base HP and, even though its defenses are decent, without investment it gets OHKOed by powerful attacks. Fighting attacks are extremely common in this meta as well, so it has a hard time setting up. Even if it does, it still lacks the raw power to break through walls. For example, a +1 LO ice punch vs standard gliscor has only a 50% chance to OHKO--this is a 4x effective +1 LO attack! Max defense gliscor has only an 18% chance to be KOed. Crunch meanwhile does barely 40% to this same gliscor. I can see scrafty as D tier, but even C tier is honestly too high for it imo.
Ahem.
Alrighty, I'm usually a nice guy and all, but I'm going to say D-Rank is too low for Scrafty. Scrafty does have flaws that make him very hard to use, yes. He is somewhat weak and slow even with the boost, but Scrafty can wreck teams. While Scrafty does get wrecked by the myriad of Fighters before the boost, he can pull off a nice sweep with the proper support. Because Scrafty usually cannot hit hard enough after a single boost, Deo-D support is necessary to ensure Scrafty does get those KO's that allow him to get dem Moxie boosts. He also needs some teammates to help him deal with some shit before he gets going. Of course, every Scarfer and some things like Starmie, Zam, and shit can outspeed him (but the things that naturally outspeed him really can't do much damage back to him in return.) Scrafty also needs to come in on, say, CBTar or ScarfGar, to get the boost in time.
But my point is here, with the proper support and timing, and skilled play, there is
very little that can stop Scrafty from devastating the team in a moment's notice. Scrafty may have trouble frequently, but with smart playing, enough support (which Scrafty needs TONS of), and all that, Scrafty is more than capable of pulling his weight.
"Pokemon that can be effective given the right support, but either have crippling flaws that prevent them from being effective or are completely eclipsed by Pokemon in the higher tiers."
Sounds like Scrafty to me.
Also, I'd say this pants lizard fares better in OU than the two current D-Rank Pokemon; Chandelure and Kabutops, who really are so damn niche it's not even funny. Then again, Scrafty is admittedly up to par with the other C-Rankers like Sandslash and Metagross IMO.
But that's just from my experience from using this guy recently.