Rampardos > rock types?

DPS wise, yes, but its also glassy, around the same level as alakazam. Its good but faints a lot more often than tyranitar

Looking at 0/0/0 rampardos and 15/15/15 SD tyranitar V double psychic lugia raids, rampardos dies 38 times (thats for a perfect, imperfect (0/0/0 its 49 deaths)), while tyrantiar dies only 14, with time to win being 830 seconds for rampardos and 992 seconds (against other sets, the number of deaths do change, but tyrantiar always has much better survival). It is powerful yes, but full teams are impractical (as most things rock types are effective agaisnt rarely carry fast moves the rock type resist (aside from fire types, which are weak to water types like kyogre), only ones I can think of are scyther, moltres, entei and other pure fire types, many times its the rock types secondary typing that gives resistance, like Tyranitar's dark against lugia's psychic/houndoom's dark and rhyperior's ground against zapdos' electric) or they take neutral damage.

Best case senario for Rampardos is V moltres (against entei theres kyogre and other water types, and against Ho-oh, tyrantiar fairs better against Extrasensory and steelwing, only HP Bug will possibly end up worse for tyranitar, as HP fighting is also SE on rampardos) with FS/HW where rampardos has 13 deaths and Tyranitar has 9, TTw is 322s rampardos and 390s on tyranitar.

Regardless of the match up (aside from HP bug ho-oh), tyranitar will be tankier, and this less are needed. Rampardos has better DPS, but its not really a case of one is better than the other over all, both are better at certain things. We dont say Gengar's better than tyranitar or vise versa, both are good for what they do, and what they do are two different things, being high DPS or being tankier. The problem rampardos runs into is stardust costs that make a team of them impractical, or reviving full teams to save on dust consumes time in raiding, balancing both Tyranitar's bulk and rampardos' DPS will be the way to get the best rock attacker, similar to how a full golem team or full tyranitar team wasnt the best during zapdos day

EDIT: the lugia numbers may have included dark.moves (double rock's preformance around 1020s in TTW), but the superior bulk of tyrantar still stands, its no different than double dark compaired to legacy gengar v mewtwo

You're giving IV's way more credit than they deserve, and that's coming from someone who chases high IV Pokemon. Simulating against a Moltres, a 0% Rampardos at L40 has ~9% more DPS than a 100% Tyranitar at the same level, although at the cost of nearly half the TDO.

Not to completely write off the weight of IV's: a 100% Rampardos has ~15% more DPS than Tyranitar at only the cost of about a third of the TDO. So yes, a 0% Rampardos will still be the best rock type attacker but unless you literally only have 0% Rampardos's I'd use better ones.