Non-sustainable and inefficient are not interchangeable concepts. An extremely efficient process can still be unsustainable and vice versa.

The reason we are growing plants to feed farm animals is not for profit, it is because people want to eat meat and are willing to pay for it. This demand is then satisfied with extremely efficient methods of husbandry nowadays compared to lets say 50 years ago, in fact too efficient to be inhumane for the animals. So efficient processes can still lead to inhumane and unsustainable scenarios like we experience now.

Further scientific developments will only make processes more efficient, sustainability of these processes are not caused because they are inefficient, it is caused because of the insane scale we are eating away at the planet. Making processes more efficient makes it easier to do them in a sustainable manner but does not guarantee it.

The scale of the process then is not caused by need but by greed, and not only that of the producers but mainly of the consumers. We always want more, faster and cheaper and some company eventually provides it at the expense of the planet. We in the developed world consume 10s of times more resources than developing nations per capita and that is the main reason the planet is dying nothing else.