It's a shameless copy.. but I like it.
Just because it's a city on a hill that has horses (like every city I might add) does not make it a copy. When constructing a city in hostile territory (as the Nedes were) you would chose high ground every time, especially in the middle of plains. Rohan lacks said nedes' boat hall, known as Yorvaskyr. Also, I don't think Rohan had a werewolf altar or a timeless forge like the Skyforge. Furthermore Rohan also lacked anything resembling the Gildergreen or a temple of Kynareth, or of any sort. Rohan also didn't have water running through it, had walls of wood not stone, and wasn't built to capture a dragon in its keep. When you look beyond the general similarities, hill city in a flat area with a horse emblem, to the specifics, everything else, you find that they are nothing near copies.