Comparing the Scoopers with JetRangers is pointless. No-one is arguing that the two perform the same work.
Comparing a '415 on a 20+ minute turnaround to a Huey with a 1400 litre bucket on a 2 minute turnaround ..... is a far more reasonable situation in realworld firefighting.
Going back to the original topic, we should ask what the Canadairs would bring to the party that we (or Victoria) hasn't already got.
High productivity aircraft operating off open water sources close to the fire? Yep, got that covered with the Aircrane and multiple helitacks.
Flexible fixed-wing capacity capable of operating off agricultural strips and laying long-term retardant line, or first-attack or fresh lightning strike. Yep, ATs and Dromaders.
What I expect (and granted, i cannot say that I've worked with machines of this capacity) that a large airtanker will do is add the capacity to lay a retardant line of significant length in one pass. This is can be used to limit the forward spread of a fire which has already begun to develop, but is not running hard. It can also be used to provide a break along the edge of a township that is threateded by fire. It won't stop a hard-running fire, but will reduce the radiant heat faced by fire crews and residents attempting to defend homes.
The '415s do not have this capacity. You can't scoop long-term retardant, it has to be premixed and pumped on board. Your capacity to reload is limited by your ability to position batching and pumping equipment to a convenient airstrip. If it takes 90 minutes to physically transport the equipment and set it up, then that is the minimum time taken before your small or medium capacity aircraft can commence to reload after its first drop.
As for "garden hoses"? If we can't do something with 3 ag planes carring a combines 7500-9000 litres, it's hardly likely that a '215 or '415 carrying a maximum of 6100 litres is going to do more when operating off the same strip and under the same conditions. The other nice thing about the ag aircraft is that we can hire them on a "call when needed" basis, which means that we don't have to pay their costs during the quiet seasons. We DO have a "vested interest".... The interest of the taxpayers who have to fund the exercise.