The LATs or light air tankers when loaded are close to their max operating weight and performance suffers. The VLAT that was in Oz a few years ago was carrying 40,000 litres and still well below max weight and performed very well with a full load. The operating cost was only just more than the LAT's and delivered nearly 4 times the load. LAT's say loads from 10,000 to 15,000, usually their drops are around the 10,000.
My experience is the LAT's loads are delivered not heavy enough, they string the loads out and don't get enough coverage. Many times SEAT's (single engine air tankers) are called to reinforce retardant lines or to tackle where fires have burnt through lines. Never had to do that with the DC10.