I definately agree the strength of Uruks (Both Isengard and especially Black Uruks) is inordinate given the information we get in the books. For a reference on how Uruk-hai fare in combat against dismounted Rohirrim, see the chapter dedicated to the Battles of The Fords of Isen in Unfinished Tales. Both sides take heavy casualties, although the orcs considerably more, and at one point, a shield wall formed by the Rohirrim was unable to be breached by the Uruk-hai, requiring the intervention of Saruman's Dunlendings.
Given this information, and for the sake of gameplay balance, I think the standard warrior of Rohan and a standard Uruk-hai should be roughly equal in capability. Of course exceptions to this would be made in the cases of special units like Beserkers, Marshals, etc.