I get your drift (I think).
Let's look at it another way. If a machine tool is exposed to water, and the resulting rust is so shallow that it can be wiped off with the palm of the hand, I can see how the machine may not have been damaged. However, if the same water managed to penetrate critical areas, it most likely would not evaporate quickly. That may cause damage that isn't obvious to the eye, and may not even be apparent when the machine is operated. Such damage may well rear its head at a later date. Could be it would be a forgiving situation--with the machine still viable and capable of producing work as intended. That, no one can say.
The picture shown is certainly not that machine. Far from it. It most certainly was altered by the elements to which it was exposed. I could not pronounce it rusted and clapped out, but that much rust certainly raises a red flag for me.
Do I think such a machine should be scrapped? Probably not. It is certainly possible to resurrect the machine so it functions to some degree of satisfaction, so that decision should be left to the individual who will operate the machine. Will it serve in the needed capacity? Will it make parts that are acceptable, or will it demand constant fiddling to get the machine to perform its intended task? Assuming fiddling will be required, is there any assurance that the machine will yield acceptable parts on a reliable basis? If not, I propose to you that the machine is certainly no longer worth owning, but that's simply because the world in which I was trained demanded perfection. It was difficult enough to master the operation of acceptable machine tools without introducing equipment that was not capable, with success achieved strictly by chance.
So then, wars and other situations offered are interesting, but that doesn't change the fact that that rusted machine is most likely to have been diminished in capacity. Some of its useful life was taken by rusting. Maybe all it had left. I don't know. You don't know, but to allow sentiment to override reality is not in anyone's best interest.
Assuming one is to go through the drill of eliminating the rust, as was done, should it ***really*** be represented as a restored machine? (I don't know---was it?)
I don't think so. It appears to me that to be fair to all concerned, it should be represented as a cleaned and painted machine. It also does no harm to keep in mind that paint adds nothing to the quality of a machine tool (although I am quick to say it certainly makes a machine look better). It may look better, but if it doesn't perform to the design level, it's not a restored machine.
I've operated old machine tools. Some of them operate perfectly well, assuming one is happy to operate within the terms of the era from which the machine came. A good example of that was the old Heald model 72A internal grinder (circa 1920) that was used for grinding the bearing housings for the guidance system of the missile. In time, a newer (but still used---circa 1952) machine took its place--a model 252 Heald. Production level doubled, simply because the more modern machine was easier to operate. Both machines were very capable of holding the .0002" tolerance required of the grinding operation.
For lathes and mills, keep your expectations in the time period, and be happy with spindle speeds that are often woefully lacking, certainly too slow to benefit from the use of carbide, and often even HSS. If you harken back to the era of WW I, with all respect to the machines of the time, they are of little use in today's world. Yes, there are exceptions. And, no, I am not down on those who own those old machines. I'm simply trying to address the reality of owning old machine tools.
If one gains nothing else, more acceptable spindle speeds are now available with import machines. They won't rival the quality of the old American built machines, but they are no longer at one's disposal. Neither are buggy whips.