On flights of 2 hours, they have nothing much to do as the drinks service takes very little time, then they try and sell tax free goods that does not seem to take very long. I consider they have so many crew that there is nothing for them to do for more than half the flight time. 3 of them to do just a drinks service in a tourist cabin of 78 seats. I would have thought one could easily have done that in 2 hours.
There are legal minimum cabin crew numbers set by CAA. Broadly speaking, it's one cabin crew member for every fifty passenger
seats on the aircraft. Up to 100 seats, you can have two crew. 101 seats would require three crew, etc.