I agree with your points - they're all well-reasoned.
What I haven't seen mentioned is the case where the drone arrives first and it's video shows the dispatchers that the fire is much larger/more involved than first reported so the dispatcher can roll additional equipment to the scene while the original trucks are still en route. That would be a major plus for having the drones.
Similarly, if the drone finds that the original report of a massive fire is more like a tiny shed on fire, they could cancel some of the equipment en route, freeing it up for other calls.
Another case: A train derailment or tractor-trailer accident. Much of the cargo carried in tank cars is in some way hazardous, and it would be very handy if a drone could show the dispatcher what placard numbers* are involved so that they can coordinate cordoning off the area and possibly evacuating residents. It would also help in making sure you have the right firefighting chemicals around - lots of hazardous stuff requires foam to extinguish and reacts rather violently with good old H2O.
*If you've never read the Emergency Response Guide, you should. Some of the nasty stuff that's hurtling down the highway next to you is very dangerous and/or toxic. It's eye-opening, to say the least.