I played through the single player on normal and I thought the throne room/Radec fight was an absolute bitch. But the strategy I had success with was a combination of IGN's strategy guide and my own lucky discovery:
For the rocket launcher guys, you have to go up to the upper level on the right side of the room and hide behind the stair railing and rubble. The rockets will mostly just blow up over your head or hit the railing before they get to you. In between, you can pop up over the rubble and pick the guys off with your sniper.
If you use the flame thrower on Radec you will beat him in less than 5 minutes. If you get in some really good shots, he will continue to burn even when he's running around invisible. That means he will continue to take damage AND you will always know where he is. The trick is finding a flame thrower laying around.
PS--I agree with you guys--I played through Ninja Gaiden 2 on the 360 and that last boss is ridiculous. I eventually did beat him, but holy crap it was hard.
