One popular plot is the discovery of a common enemy that forces Superman and Homelander to team up, despite their differences. Another is a battle for supremacy in a world where both exist, with different factions taking sides. And then there's the plot where Superman tries to reform Homelander, seeing the potential for good in him.
Well, it depends on how the fanfiction is written. If it's a more 'grounded' version where Homelander's public image and mind - games play a big role, he could potentially gain an upper hand. But generally, Superman has more raw power. He can move planets, and his speed is almost limitless. Homelander is strong and has flight and heat vision too, but Superman just seems to be on a whole other level in terms of pure power.
We don't have enough information to know exactly who Marie is in this story. She could be an ordinary woman with an interesting life, or someone with a special talent or gift.
I'm not sure who Marie specifically is in 'Marie the True Story' without more context. It could be about a real - life individual named Marie, but more details from the story would be needed to accurately define her.