At the moment, as of 9/11/2018, Arwen feels indispensable for getting max score. I'm not saying its impossible, but I think her healing, plus her 3 makes her perfect for the job. She feels like the digital equivalent of spirit Glorfindel.

Now, at current difficulty, I'm not sure that that is a bad thing. Her innate ability allows 275 on hard to feel possible. I've taken Éowyn merely for her 3 , and she offers that with a bonus. At the moment, I think there is no doubt that she is the strongest hero in the game.

I've done a whole campaign of max scores without Arwen. With Faramir for lore access you can get enough healing to end at full health every game. —
@Seastan I'm aware it's possible and people have done it, but arwen makes it almost easy. —