>>38220671rock is garbage. its a great offensive type, but most non rocks can use stone edge/rock slide, so rock types dont have that niche. nintendo tries to make rock pokemon defensive, but thats not the kind of matchups that the type has. if rock had less weaknesses then it could work, but so far the only pokemon that could be both rock type and defensive is ttar because his stats are ridiculous and later on because of sand stream. Even then, ttar works in more ways than just defense, if anything the defense is an added bonus.
tl;dr if rock had less weaknesses it could be better.