Ok that's more than enough bickering about Amoonguss. Tsk tsk children, I expect better of you. Anyway, Tyranitar certainly does quite a lot, and I can see why people are arguing it for S-rank. Sand Stream is a very potent ability, not only having a host of benefits that make it useful on its own, but also helping check opposing weather. Tyranitar is really well-suited for supporting roles, whether as a Stealth Rock user or Pursuit trapper, and it's no slouch offensively. However, it has very notable flaws that prevent it from being S-Rank, in my opinion. The first and foremost is obviously that defensive typing. While Tyranitar's special bulk lets it get away with handling most of what it needs to, it is plagued by weaknesses to very very relevant offensive typings (Water, Fighting, Bug, and Ground being chief amongst them). Tyranitar can very often perform its roles, but after doing so it invites openings to things you don't want to give openings to, such as Keldeo, Terrakion, Landorus formes, etc. Or you could just get sniped by Dugtrio. This is doubly problematic in that Tyranitar has a hard time being a supporter and providing an offensive threat at the same time. Stealth Rock and Scarf sets don't pack nearly the wallop of CB, making them more of a defensive liability. So while Tyranitar is an exceptional supporter, I feel that its very notable weaknesses hinder it enough to keep it in A-rank.