Tyranitarite, Choice Band and Assault Vest are the best choices on it, but it ultimately depends on team.
Your team doesn't have any Pokemon capable of Mega-evolving, so it's definitely not causing any overlap. Mega-Tyranitar gains a decent boost to its Atk, and a solid bulk increase. It has both offensive and defensive qualities, with the stat boost combined with a single Dragon Dance can sweep easily. The extra bulk means it has better defensive capabilities vs Pokemon such as Mega Latios, Mega Charizard Y, Heatran, etc.
Rockium Z is still more of a niche. If you need to hit hard, then that's what Choice Band exists for. A one-time blow isn't always the best; Tyranitar has pretty common checks and counters. Defensive Landorus-T and Hippowdon can easily tank a Continental Crush unboosted and force to switch out because of Earthquake. CB also outclasses Black Glasses in that aspect.
Mega-Tyranitar can set Stealth Rock in Bulky Offensive teams. However, Assault Vest is also an option that has more defensive utility.
Assault Vest allows Tyranitar to become an effective check for many of the tier's most threatening special attackers such as Mega Charizard Y, Mega Alakazam, and Heatran. 224 HP EVs allow Tyranitar to avoid the 2HKO from Mega Latios's Earthquake—this investment in combination with maximum Special Defense investment allows Tyranitar to tank even some of the strongest special attacks in the tier such as +1 Savage Spin-Out from Volcarona with Assault Vest.
tl;dr use Tyranitarite or Choice Band for offensive purposes, and Assault Vest for defensive utility.
As for the team, most of your Pokemon aren't good in SM OU. Talonflame and Decidueye are not even ranked, while Alolan Ninetales is on the bottom of viability. Your team doesn't support Tyranitar that well nor benefits from it; for example Sand Teams with Tyranitar / Mega Tyranitar run Sand Rush Excadrill and Garchomp.
I suggest that you should read the viability rankings first, and then start building something more suitable and workable around Tyranitar.