yeah tanks or ranged dps are generally best suited to this job, melee dps are completely blind for the most part
Tanks are essentially group leaders, since they're counted on to manage the pulls and the flow of the fights. They are also always on the boss, and most aware of mechanics and when they will occur. I don't really think it's "expected" for tanks to assume the leadership role, but most do out of necessity.
RDPS make the best raid leaders in my opinion. They generally don't need to avoid fight mechanics and their rotations are systematic. Additionally, because they're further away, they have a better view of what's going on. In a lot of encounters, the boss fills the entire viewing area of the tank.