So if you're growing soy on deforested land as a base for your "cruelty free" burger, it is very possible that this has damaged the original ecology (and killed living things) more than having grazing cattle would.
Exactly. It's not like animal husbandry and meat-eating developed as some kind of ostentatious wasteful consumption. It's a way of converting inedible plants into edible meat.
Is it true that everywhere we have cows we can also grow soy or wheat or whatever? No, definitely not. Does that matter? No, definitely not.
Further, some of that land which is unsuitable for growing crops used to be - and was degraded by growing crops or grazing. Further degrading and depleting it doesn’t do us any favors.
The point is that grazing is much less destructive to the original ecology than farming, so it's not clear that 1 acre of farming is better than 100 acres of grazing.
I might be misguided here, but AFAIK grazing doesn't "deplete" the land at all (and might even improve the land with manure / etc), where as farming absolutely does unless you're careful about it.