Several things
Yes aircraft are paid for standby, the alternative is not to have those aircraft available. Current situation an example, Victorian aircraft could be utilised in NSW which would make them unavailable for dispatch in Vic. Not sure where you got your figures from but SEATs are getting less now than they were 10 years ago and certainly less than you quote, would you recommend to cut costs and maintenance on aircraft that work so hard in hostile conditions? Obviously you don't fly on fires going by your conjecture.
Just say your idea is valid that aircraft are useless in most fire situations. Leaving aside attacking the fire. From personal experience I have seen on many occasions where aircraft have been utilised on direct attack on vehicles and assets under a dire threat. Calls have been from people in vehicles for drops on vehicles, I have seen both foam and retardant used for this, depends whatever the aircraft has on board when the threat is called in. The events I've seen there was no other choices for ground crew intervention. How would you suggest to have aircraft ready for such situations without a standby?
Again I don't know where you get your information from, aerial drops are authorised from the fire ground controller on the fire who is also controlling crew, or from an air attack supervisor flying over the fire who is in contact with fire crew and the fire ground controller. NOT from a command centre many kilometres away. If there are no ground crew the aircraft pilot has authority to drop after the usual checks and inspections are made. Aircraft DO NOT just go in willy nilly and drop without checking out the area.