I have run threw more cassettes that I can remember, ultegra has done well for training and so long as regular chain replacement is done they last 3 to 4 chains.

Lower end cassettes wear quicker and I tend only get 3 chains out of them.

I don’t ride much with dura ace cassettes, I doubt that the cassette would last longer then ultegra. If it did then it would need to wear 2x slower then ultegra to make it financially justifiable for training.

For racing, the extra weight loss is easily justified considering how difficult (costly) it is to reduce weight on wheels. Rotational weight is key during races with lots of spin ups.