The retardant aircraft and scoopers have different roles and contrary to popular belief, often neither solely focused on extinguishment of a fire of any great magnitude. The red retardant is primarily used for containment, establishing a defensive line just ahead of the fire. The desire is not so much to extinguish fuel that's already burning but more to rob the fire of additional fuel once it gets to the line. It can be used as an initial attack tool to buy containment time until other resources, such as ground fire fighters, helis and heavy equipment can get on scene. Retardant is also used to create protection lines around structures and other values. The scoopers, in my limited experience, are more commonly used to modify fire behavior in support of ground based resources, or to defend the fire lines if there have been excursions through the line or windborne spotting across the line. Much like municipal fire departments working to prevent a house fire that is a total loss from spreading to the rest of the neighbourhood, it's often a more effective use of resources to starve the fire of new fuel rather than attempt to extinguish something that's already fully involved.