You can defeat enemies with lots of health, easily by using spirit attacks. The armor only defends against melee and ranged attacks.You can also use attacks that ignore the armor, like targeted strike(Berethor).
To get all spirit powers for idreal, and mayby the others with the Elf stones (im no completely shore), it take a bit of time.
Firstly you will need to get her 'Drain inspiration' and go around about the fellowship camp in eregion. Keep looking for a battle and when you get in one with a Orc lesse Captian (the one with the white hand on some fabric on a stick) and use Drain inspiration on him. He will not attack you because all his moves require sp. This way you can keep using Drain inspiration to get action points for spirit powers.
Again, this may work with an elf stone that does this but I'm not shore if the stone excists.
First you have to complete the game once (you don't have to get all the attacks, just beat Sauron at the end of Pelennor fields.) Then start a new game. Save it and exit.
At the main menu, go to more, then evil mode. Load it as your completed game. Select a level, e.g Minas Tirith, and do the level. When you get your stuff save it to your new game. Then load up your new game and go to 'Equip'.
If you do Minas Tirith, Berethor should have the best lower body armour he can get ( darkened Numenorian steel fauld, armour:68, 5star.) Also he should have Sword of Isildur, High king of Gondor, damage: 205, 5star.