so for the anode it is to prevent the tank from rusting out and springing a leak.
It seems you water isn't causing as much corrosion as others. That would be an interesting thing to check. most local water sources provide a water quality statement.
ours is pretty hard water.

the flush though is more for efficiency which may in turn shorten the life of the tank or heating elements.
I would be interested to see how much build up was the reason those other heaters died. couldn't heat the water anymore vs actually not "working".

if you are using electric or gas there might be a difference too.
gas has the whole column that heats, so you might get away with the bottom filling up with sediment and not notice longer than say an electric with only 2 heating elements that might be buried.

the most expensive rods are only 25 bucks. every 5 years or so if you can get away with that. they generally are around 10 bucks.

I would say pull one and see.
next time one dies, I would see if you can cut into the side and see how "full" it is.