Tyranitar down to A- rank
Tyranitar isn't what it used to be.
For a Scarf and sweeper (DD) role, it faces competition from Mega Diancie and Terrakion, who compensate for less bulk with more Speed that does not require the aid of Scarf or DD. In Diancie's case, it hits much harder too with a much better spread attack than Rock Slide. DD sets also require team support
Tyranitar's bulk is hindered by the vast amount of ways to hit it super-effectively (19 of the 25 pokemon in S and A rank commonly have a move that hit it super-effectively). This, combined with its Speed, makes it a bit awkward in the metagame where so many Pokemon threaten it. This is probably the most important point, despite Ttar's potential with its vast versatility. Even though it can do beat so many Pokemon with the right set and moves: it can beat Ground-types with Shuca Berry + Ice Beam, it can beat Steel-types with Low Kick and Fire Blast, it can spread pain with both its STABs, but it cannot do everything at once, and that's an issue when so many things can potentially threaten it (and some like anything with the Fighting-type will always win).
Dark-type is good for coverage against Psychic- and Ghost-types, but even then, it faces competition from other Dark-types like Bisharp and Aegislash who both hit harder with their STABs and have more useful perks like benefiting from Intimidate (Bisharp) and much better defensive typing (Aegislash). Also Tyranitar fails miserably against Metagross.
Sand Stream is useful for benefitting Excadrill. Unfortunately, the two share common weaknesses that can dismantle the duo, unlike say Politoed + Ludicolo. And when the two are paired together, Excadrill is easily the more threatening of the two.
Since when has Heliosk been outside the E rank?