Ok after many battles he does use his other attacks but rarely.
i always thought they went right to left on their moves in auto.
it's a bit more complicated than simply right to left. each champion has their own specific instructions programmed regarding skill priorities. often they do simply go starting from the right, but there are plenty of champions who don't follow that pattern. there are also many champions who change which skill they prioritize depending on the circumstances of the battle they're in. rotos, for example, will prioritize his a3 if there's a target available who is low enough on hp that he can likely kill them, thus triggering his extra turn. otherwise, he will use his a2. while i've never used ruffstone, i suspect he works similarly. my guess is that when there are several enemies alive, he will use his a1 since it's an aoe attack and will start using his other abilities when only one or two opponents are left alive.
How can a champ that attacks the whole team every time be avg?
how can a champ that hits a single target for a lot of damage be average? how can a champion that heals your entire team be average? how can a champion that revives dead champions be average?
the answer to all of these along with your question is that that's just another ability. some champions with it will be great, some will be just okay, some will be trash. aoe attacks on a1 isn't even a particularly rare ability like poison sensitivity or increase skill cooldown. it can be helpful, sure, but it's not generally a gamechanger.