Breaking it down;
We will have 4 tanks
We have 4 melee dps
We will have 3 ranged/support dps
We have 3 magic caster dps (4 if you choose to include BLU, which for now I won't since we'll look at this as a max level spectrum)
We have 3 healers

Really, Dancer being a ranged dps/support makes sense since it was the class that had the least when it came down to numbers specifically. Plus I think its nice to have a ranged member who will bring more slashing damage in so it should fit decently well in groups, just my two cents really.