Tyranitar's stats are actually still excellent. It's just that its STAB combo and base typing are don't cut it offensively (Great Tusk, Zamazenta, Kingambit, Iron Valiant, and Ting-Lu) or defensively anymore since this generation saw an influx of offensive Ground, Water, and Steel-type Pokemon in OU with mons Tyranitar used to check well in OU, such as Blacephalon, Heatran, Slowbro, and Tapu Koko, either being dexited or nerfed heavily, making Tyranitar's niche less important.
For reference to TTar's huge special bulk, here are a couple of calcs which show that TTar actually takes strong attacks such as Walking Wake's Draco Meteor better than Ting-Lu does, meaning its stats aren't the issue:
244 SpA Choice Specs Walking Wake Draco Meteor vs. 252 HP / 252+ SpD Vessel of Ruin Ting-Lu: 192-226 (37.3 - 43.9%) -- 99.9% chance to 3HKO after Leftovers recovery
244 SpA Choice Specs Walking Wake Draco Meteor vs. 252 HP / 252+ SpD Tyranitar in Sand: 148-175 (36.6 - 43.3%) -- 98.8% chance to 3HKO after Leftovers recovery
Actually, Sand Rush still gives Excadrill a niche it has over Great Tusk since it'd be able clean weakened teams with its very high speed in sand. Yes, Mold Breaker gives it a better match-up into Hatterene since she can't bounce its Stealth Rock back, but to suggest that the only thing Excadrill has over Great Tusk is its match-up into Pecharunt is a completely incorrect statement even though Great Tusk is admittedly a much better Pokemon.