There are approximately 1 million feral camels in Australia. Their ancestors were brought over in the mid 1800s because of desert conditions. Sheep are also an imported, non-native species brought over in the late 1700's. There are between 100-120 million sheep in Australia.
Camels eat less and conserve more water than sheep. They drink less than sheep and goats. They eat less per their body weight as well.
Sure, camels are nonnative. So are most of the humans on Australia. And the sheep. The latter two, so far, have caused a lot more damage to the land and consume more water than camels.
So, while I agree camels are probably causing some annoyance to farmers, I am not buying that they are the primary problem species nor am I buying that shooting 2/3 of them is going to solve the water issue in Australia.