Aramusha lvl3 is probably the most irritating to deal with, I agree.
And some of the parry timing is really awkward compared to the relative standard elsewhere in the game. I imagine that was to make the character more "challenging", sort of like Cent. Can't really guardbreak his heavies on startup either. Again, sort of like Cent.
Just give it a while; practice to get the parries and watch your distance. He's only a bad menace if you let him get close.