Unlike most characters with sharingan, oro would use it to its full potential.
He would put anyone in genjutsu that looks into his eyes(itachi), genjutsu wouldn´t work on him anymore cuz he would see through most genjutsu except for high level ones like Tsukuyomi and kotoamatsukami, he would copy all of the opponents techniques(kakashi) + he´s got his own forbidden techniques to use not to mention edo tensei.
He would have made sure that he has izanagi cuz if oro helped danzou get hashirama dna for his izanagi then we can safely assume he would do it for himself, he can´t really get hurt anyway and if he catches amaterasu he´ll just shed his skin, he´s got alot of huge summonings, earth and wind element, his other snake jutsu and if he´s about to lose, he can just summon a snake and get in its mouth while teleporting away.
No ninja would **** with oro if he ever had the sharingan and i think the reason kishi made it so he doesn´t get it is because he didn´t want him to overpower all other ninjas as that would destroy the plot, he never showed oro at full strength and even then we´ve never seen him go all out, most of the time, he just played around.
Madara would probably still win but he would be near-death himself when it´s over.