Colossoil has STAB Earthquake
Colossoil has immunity to Electric-type attacks
Colossoil has Guts
Colossoil has Sucker Punch
Colossoil has Rapid Spin
Colossoil is a whopping 34 base Speed faster than TTar
Colossoil is not 4x weak to Fighting-type attacks
U-turn
As you may know,
Tyranitar gets STAB Stone Edge (which is better because it has no immunities, in comparison to EQ)
Tyranitar has a Fire resist
Tyranitar has Sand Stream
And Dragon Dance and Stealth Rock and hell, Curse and Rock Polish
Tyranitar is similarly bulky physically and quite a bit more bulky specially
Tyranitar has 12 more base points in attack
Tyranitar has much more SE coverage and a viable special stat backed by good special movepool
Tyranitar isn't Ice weak
:/
Imo, they're different pokemon, except for Dark-typiness (a big point). The only remarkably similar set they run is a Choice Scarf set, which Soil admittedly generally does better in, with U-turn, Guts, and speed. LO attacker Soil does not need to boost like Tyranitar to sweep, but has significantly less power. Lead Tyranitar has Stealth Rock and Sand Stream to break sashes, Colossoil has Rebound, Rapid Spin, and U-turn. CB Soil is worse than CB Tyranitar (imo), with inferior STAB that lets it get set up on easily, but it does have U-turn.
Ramble, ramble. Point is, in my opinion, Soil does not outclass Tyranitar as a whole, they're just comparable because they're dark typed with good attacka and bulk.
Regarding the nerf, I like Deck Knight's spread better, because it's still fast. Think about OU, is Suicune fast? Heracross? No. Is Lucario fast? ...No, it doesn't hit 100.
What does base 85 speed mean for Soil? Well, at base 95, it could tie with Lucario [and Electivire] and outspeed Rotom-a, as well as outspeed Heatran with an Adamant nature. Is that really breaking Soil?
\/EDIT: I blame errors on coffee at midnight. Also, ow, player punch.