I agree that Raikou is better suited for offense -lightning fast speed, pun intended-, but its move pool is barely acceptable for that role, that's what keeps it from jumping to OU imo. Roserade has two STABs which give decent coverage together (Poison sucks at attacking, but it combines decently with grass), and can run Hidden Power just like Raikou. Raikou has a pseudo Boltbeam coverage, so he's obviously pretty solid, but his being great is more of a virtue of Ice being an excellent attacking type and Raikou having a decent defensive type which does good coverage with Ice. Those are not movepool advantages, that's simply great typing. Raikou happens to have an offensive movepool that's almost as crappy as Roserade (unless you run the Rash nature event), but it can carry it much better for many valid reasons. Raikou doesn't have a movepool suited to be offensive, just the opposite, he's offensive despite of his barren movepool.
And yes, running four attacking moves is never a good idea, unless you're using a Choice set (and have no better options), or you're something random like Beartic :p