As a big fan of Legends (surprise, right?) I am aware of many parts of it that others are not. But in Legends the general level of power of the Sith and Jedi alike is increased significantly. Like how there are 2 Sith that obtained the power to wipe out entire planets with the Force, and one who even made a star go Supernova. Existing characters like Luke and Sidious also receive immense power boosts, allowing them to compete with the Legends homebrews, and causing the movies to keep making sense.

Some characters are clearly stronger than others. Just a bit before Magnus was facing off against I believe 5 other characters? Any one of those characters would have lost to Magnus in a 1v1 because of the power difference. If one were to pit Set Harth against, say, Gilgamesh, Set would last a glorious 15 seconds (the length of Gilgamesh's smug monologue). Vader is one of the most powerful characters in the RP, and represents an immense threat.

That said, those feats of power require him to stand still and concentrate. As long as he's engaged in melee or dodging bullets he can't use that kind of power. Characters like Youmu have a chance of outspeeding him, and inflicting serious damage while barraging him with attacks. While Set can level the power gap through trickery, sorcery, and by finding friends. Weaker characters can topple stronger characters by playing to their strengths, or by banding together. And the stronger characters must be careful not to be too powerful, lest too many people decide to gang up on them.

In short: power differences exist, but they're not bad.

Vader is a seriously bad mofo, and should be dealt with as if he were a 'boss monster'. Lots of people working together, or confronted by another exceptionally powerful character. He could be defeated here because Set knows what he's weak to, and isn't going to let him use most of his fancy force tricks. Combined with the constant assault of the other two, I see Vader only winning barely, or more likely just getting forced back/defeated.