Since everybody is disagreeing with me, I withdraw my arguement for dusknoir. However, I still believe that scyther should be low b-rank.
Anyway, Sandslash and primeape go down to D-rank. Sandslash is THE WORST spinner in RU (even worse than hitmonchan) and has no real niche over kabutops or cryonagal. The offesive spinner set is outclassed by kabutops while the defensive spinner set is often going to be worse than cryonagal because sandslash lacks reliable recovery. Sandslash also has poor special bulk and typing, leaving it vulnerable to most special attackers. It also has poor speed, meaning that faster pokes can easily take it out. Hitmonchan may not be a great rapid spinner, but has the niche of being able to spin against ghost types with forsight, making it a slightly better rapid spinner. In the end, sandslash will usually end up being trash.
You do not know what you are talking about.
Sandslash isn't bad, people use it wrong. They slap rapid spin on a swords dance set and expect it to work.
"(even worse than hitmonchan)" No. It isn't, it just isn't.
"The offesive spinner set is outclassed by kabutops while the defensive spinner set is often going to be worse than cryonagal because sandslash lacks reliable recovery." It may be out-classed offensively, but Cryogonal and its base 30 defense... man.. the defensiveness of that! Unless of course you meant special defense, but then what outclasses sandslash as a physically defensive spinner?
"Sandslash also has poor special bulk and typing, leaving it vulnerable to most special attackers."
Its funny, because you said that cryogonal was a great defensive spinner when it has far worse physical bulk than sandslash does special, and can't even take one physical hit. Especially after its weakness to stealth rocks, and sandslash's resistance. Note that I am not bad-mouthing cryogonal, as you will see later (also I absolutely love its design) but you compared the two of them, so I am doing the same.
"Hitmonchan may not be a great rapid spinner, but has the niche of being able to spin against ghost types with foresight, making it a slightly better rapid spinner." So hitmonchan is the best spinner in the tier because it has foresight. If it out-classes sandslash in the spinner role due to that one move, then why doesn't it out-class cryogonal or kabutops because of it?
And, in spite of all that you said, you didn't even mention the fact that it can sweep pretty reliably with swords dance. Not every kabutops uses rapid spin, not every hitmonchan uses rapid spin, no hitmonlee use rapid spin and not every sandslash uses rapid spin! In the D rank decription it explains "are only capable of doing their specific task". Thus why hitmonchan is there because it only spins. But then you have sandslash, who sweeps with swords dance. On two different sets, maybe, but either way it has 2 specific tasks it can do and it does perfectly well at both, keeping it a C rank. Maybe a low C, maybe a mid C, but either way a C.
Note on the other two things you said:
I really need to test out primeape some time, its stats and typing look really nice to me.
If your team has trouble with Cinccino, have you ever tried rocky helmet ferroseed? It kills cinccino by switching in to it, since 4 rounds of iron barbs and rocky helmet kills cinccino by itself. It also completely works with the hazard setter role, I just thought I would note that since it is the only pokemon in RU OR NU that can do such a thing. (and it has to survive 4 rounds in case some anonymous weak pokemon has the right ability as well).