He would still be beatable. Pain/Nagato only used 6 different jutsus and is arguably the strongest character there is.
And having the sharingan still wouldn't help him against Itachi, or Nagato, or possibly the third raikage, maybe Minato (I don't think so but maybe).
I mean it would have given him a major power boost but honestly he had more jutsus than even Hiruzen and it didn't really help him in that fight (although he didn't really fight). There are just some things you can't beat, and having a normal 3-tomoe sharingan wouldn't help him that much except for copying more jutsus and being able to fight faster opponents.
Just look at Naruto for example, he knows under 10 different jutsus and is beating kages with a huge variety of skills. (I count the rasengan and rasenshuriken as 2 separate ones, but not the various ways of executing them or the size differences)
My point is that while Oro would have gotten a major power boost from the sharingan, Sasuke only had a 3-tomoe then, so I don't think Oro would have broken into the top 5 strongest characters. He would have moved up even further and probably been the strongest of all but the gods of Naruto; Nagato (rinnegan, insane chakra), Itachi(MS, legendary weapons), and Minato (ST, sealing, insane normal speed)