Actually Gigalith's abysmal speed (base 25) lets it down here, since I just calc'd its base stats being curious myself and got
229 Atk, 222 Def + 170 HP
vs Ttars 251 Atk, 212 Def + 200 HP
So in order for Ttar to lose the TDO advantage it would need to go up against (Flying/Ice/Fire)+Fairy type, a bug type or a Bug+Fairy type
Atm there are 3 fully evolved Pkmn that match these dual typings, being Alolan-Ninetales, Togekiss and Ribombee (and ofc the bug types)