No, Tyrantrum is not viable
Why? 1: It’s outclassed by Tyranitar. Tyranitar is a more bulky and efficient defensive Pokémon that also has access to Sand Stream. Tyranitar soaks hits Tyrantrum would die to.
252 SpA Tapu Koko Dazzling Gleam vs. 0 HP / 0 SpD Tyrantrum: 324-384 (106.2 - 125.9%) -- guaranteed OHKO
252 SpA Tapu Koko Dazzling Gleam vs. 0 HP / 0 SpD Tyranitar in Sand: 140-168 (41 - 49.2%) -- guaranteed 3HKO
Tyrantitar is also a more efficient Dragon Dancer. It can Dragon Dance and survive a hit Tyrantrum would die to.
252+ SpA Volcanion Steam Eruption vs. 0 HP / 0 SpD Tyrantrum: 303-357 (99.3 - 117%) -- 93.8% chance to OHKO
252+ SpA Volcanion Steam Eruption vs. 0 HP / 0 SpD Tyranitar in Sand: 264-312 (77.4 - 91.4%) -- guaranteed 2HKO
Imagine that Tyranitar with a Weakness Policy! Anyway, Tyrantrum is just plain outclassed by Tyranitar.
2: It’s countered by a lot!:
Here’s a few examples. This is even with a Dragon Dance.
Uber Defensive Ferrothorn(especially if you don’t carry Fire Fang):
+1 252 Atk Tyrantrum Head Smash vs. 252 HP / 252+ Def Ferrothorn: 104-123 (29.5 - 34.9%) -- possible 5HKO after Leftovers recovery and Leech Seed recovery
252+ Def Ferrothorn Body Press vs. 0 HP / 0 Def Tyrantrum: 168-198 (55 - 64.9%) -- guaranteed 2HKO after Leech Seed damage
Bulky Physical Wall, Special Sweeper Tapu Fini:
+1 252 Atk Tyrantrum Head Smash vs. 252 HP / 116 Def Tapu Fini: 280-330 (81.3 - 95.9%) -- guaranteed 2HKO after Leftovers recovery
120+ SpA Tapu Fini Dazzling Gleam vs. 0 HP / 4 SpD Tyrantrum: 312-368 (102.2 - 120.6%) -- guaranteed OHKO
Bulky Special Sweeping Heatran(Air Balloon):
+1 252 Atk Tyrantrum Close Combat vs. 252 HP / 4+ Def Heatran: 322-380 (83.4 - 98.4%) -- guaranteed 2HKO
252 SpA Heatran Earth Power vs. -1 0 HP / 4 SpD Tyrantrum: 450-530 (147.5 - 173.7%) -- guaranteed OHKO
Physical Wall Clefable:
+1 252 Atk Tyrantrum Head Smash vs. 252 HP / 252+ Def Clefable: 306-361 (77.6 - 91.6%) -- guaranteed 2HKO
0 SpA Clefable Moonblast vs. 0 HP / 4 SpD Tyrantrum: 300-354 (98.3 - 116%) -- 87.5% chance to OHKO
So yeah….. Tyrantrum isn’t viable in Gen 8 OU.
About doubles, Tyrantrum could be good with access to Rock Slide and Earthquake, but Tyranitar also has both of those, so…….. yeah. I would choose Exadrill with Tyranitar. It uses Ttar’s Sand Stream extremely well with Sand Rush and a fat 135 Atk.