Where is there evidence that wolves will kill off most of the natural prey?
There used to be wolves in Maine, and in most of the northern areas from here to the Rocky Mtns. Your idea would have it that those wolves ate everything. That is simply not true. Moose and wolves co-existed quite well and for thousands of years in the past. The most recent 150 years or so, when wolves have been extirpated by humans in most of that area, is the aberration.
There are certainly a lot of pressures working against having a natural ecological system, but I don't think we should accept converting the world into the equivalent of a very sad zoo, nor do I think we have to.