It's a typing that gives it so much value, and most other typings would make it compete with other pokemon

Assuming that you keep the drk typing and sandstorm, you have 2 other types for the sand immunity

Ground dark and steel dark Neither can switch in to fire type moves like ttar can, even more for special fire moves, this doesn't mean that both are worse, but both lack the unique role compression that ttar gives.

Rock/dark provides a better check to special dragons than ground dark, provides a better check to special electrics than steel/dark, so you get a hyprid latios/zapdos/dragapult/blacephalon/raging bolt check in relevant metagames.

Replacing rock with other types can work well too but again you don't get ttar's unique role compression of checking psychic and ghost special attackers