(...) aren't there better things to do with increased agency than to seek to dominate other potential agents?

"better" according to whom? The only one who can set a different standard for yourself is yourself, yet if you already do have that "dangerous intrinsic goal", then, well, you already do have that goal (yay tautology). You can weigh it against other goals and duly modify it, but presumably if other goals outweighed your need to dominate, that would already have happened. Since it has not (for those who have that goal), that is reason to surmise that from the point of view of those agents there isn't in fact anything better to do, even if they'd like to think that they think there was.