Omastar niche?

I think the answer depends on how well you did with the TTAR event. I have 6 TTAR over level 33 with Smack Down and Stone Edge and a full team of level 35 Golems. Omastar is not super common here and i am not inclined to invest CM to give those I have the right moves.

I'd rather have a RT/RS Omastar just because it takes Tyranitar ages to fire off a Stone Edge and it would be great against the impending Moltres raid event. It's a shame only 4 people have one. Congrats!

Worse DPS and TDO than SD Tyranitar, but it's not like it matters that often. If you like using it, go ahead and use it, it's a rare legacy that people are for sure going to envy. But I wouldn't spend dust on it over Tyranitars unless you have a lot of extra.

One of the benefits of double rock Omastar is that it doubly resists fire, and it's not weak to ice like most rock is, because of the water typing. Purely from an attacking standpoint, it's clearly not as strong as SD/SE Ttar.

Kabutops enjoys the same advantages with RT/SE against ice, but doesn't have a good move for fire.

Bottom line, when Moltres comes to town for a three hour cruise, Kyogre will shred it, SD Ttar will shred it, Golem will shred it, even Raikou will shred it. If you don't have a good counter, you haven't been playing long (which is no crime, just something to work on).