Fire bombers are meant to prevent a fire from spreading by attacking a flame front before it gets too intense, but whatever is burning behind is essentially lost. The effect goes past the point of merely putting water on the fire, but of flushing an area with 6 tonnes of liquid.
Using water bomber on a building would essentially destroy whatever is left of the building, and that is precisely what the fire fighters on the ground were trying to do: save the REST of the building.
Moreover, water bombing would have required for all firefighter to move out of the perimeter for safety reason, which would have meant to stop trying to salvage the art they were trying to get out.
Not only would have water bomber be useless, they would also have been extremely dangerous. Water bombing is not done in a city, and certainly not at night. Picking up water requires half a kilometer of straight water body, plus clear approach and depart path. The river through Paris is meandering like crazy, and there are bridges every 1000 feet.
Add to this the fact that it takes about half an hour to get crews ready, start-up the plane and organize flight path, plus the time it takes to fly from the bases (which are kept close to *forests*, not to cities) and you would have planes on site after the fire is out anyway.
Meanwhile, a single properly fed fire hose can put out as much water in 10 minutes as there is in one air drop. How many fire hoses were there in action?
What could water bomber possibly add?
Forest fires are a completely different problem, since they are uncontained (there is 'fuel' everywhere) and they will spread; on the other hand, given that the church is surrounded by streets on all sides, the risk of the fire spreading was essentially zero. Forest are also pretty much devoid of fire plugs, and hard to access with truck, ladders and fire lance, that is why they are attacked form the sky (and again, ONLY DURING DAYLIGHT).
Trump is an idiot, and that he 'proposed' something amazingly stupid does not make it brilliant.
It was a stupid idea for a moron.
Associating with it and defending it will also picture you as an ignorant.