> and do so quite inefficientlyMatter of perspective. Compared to carnivores, all herbivores are "inefficient". A wolf (even humans) can gulp down some 1-2 pounds of fatty raw meat in 10-15 minutes and be done with eating for the day. Doesn't even need any manner of dentition if pieces are pre-cut to fit the tube into the stomach.
Put on another lens though and ruminants can be seen as profoundly "efficient" when look at the actual nutrient density of grasses and seeds.. with their micro-organism colonies they also synthesize various vitamins/vitamers that mammals need but grasses/seeds/soil doesn't provide.
But yeah grazing and ruminating all-waking-time isn't terribly "efficient" from the viewpoint of us goal-oriented or creative mammals.
> the only thing animals do is save time, when we were naked and running the meadows, other animals collected nutrients for us, stored them in the bodies and saved us extreme amounts of time.
Again, they can also break down cellulose which homo sapiens never could do, so it's not just "saved time". Thus herbivores can liberate (the majority of) micronutrients from vegetation that we cannot even access (except perhaps a few in a stew for the non-heat-sensitive vitamins, and a few in the juice run-off from certain fruits or leaves when mashed, bitten or squeezed or such). Finally they synthesize vitamins we cannot synthesize no matter what gut bacteria we host. Again, capabilities that go beyond "saving time".
> currently, most of the animals we eat are just inefficient in converting edible to edible, soybean to meat
What animals are fed soy beans, hopefully only pigs and not ruminants (grasses/seeds eaters)?
You're not converting "edible to edible", you're converting "barely palatable (save for hours of pre-processing and time-consuming cuisine theatre) to eminently, utterly enjoyable and fully nourishing + highly energizing, even raw" --- the animal takes a lot of time but the human is free to pursue other undertakings. There's no serious need to "speed up food animals" as long as plenty of them are kept.