>>55740239rock is generally a shitty defensive typing due to its weaknesses to common attacking types (fighting, ground, water, and grass) as well as steel, which resists it
those weaknesses are shared with a lot of types that would be good on mons that didn't have to be part rock, like steel, ice, electric, fire, water, etc
basically the only rock types that are good enough within the last 2 gens to not be in a tier below UU (inb4 "muh fanfic" fags even though most mons that are shit in smogon's various singles tiers tend to also be shit within the official battle spot/VGC metagames which don't even have usage based banlists to give weaker mons tiers in which they're competitively usable) are hisuian arcanine, arceus-rock, garganacl, glimmora, ogerpon-cornerstone, and tyranitar
and all of those are all in UU or above because of other qualities that aren't just "is part rock type)
hisuianarcanine has recoilless head smash + flare blitz + espeed + close combat/stealth rock
arceus-rock is an arceus form
garganacl has a great ability and signature move while not having a secondary typing to give it weaknesses
glimmora is a great lead with good special attack and the ability to setup layers of toxic spikes when hit, possibly in the same turn as using stealth rock
ogerpon-cornerstone has a decent sub-type and a good movepool (and ability when terastalized)
and tyranitar is a weather setter combined with a great movepool
only one that could be considered decent due to being part rock is hisuian arcanine because of STAB head smash, but unlike other head smashers, Arcanine has good coverage, a decent speed stat, and decent bulk to ensure it'll get to head smash things at least a few times
