I'd argue that China, Russia and the US have already passed this point w.r.t. nucelar weapons: Every side is sufficiently armed so that a war between any of them cannot be won. As soon as you start winning in a conventional scenario the other side might as well use nuclear weapons, just to ensure you'll lose too. In short a war between nuclear powers makes no sense, since the "victory condition" has been removed.

I'd assume that this is the same in asymmetric conflicts: If you are fighting a guerilla war, you "win" when you kill some of your enemies troops and demoralize them. However if enemy sends only machines, then cannot win as long as the enemy is capable of producing more of these autonomous weapons than you can destroy. As you've said the cost savings do enable that. Hence the guerilla side also loses its victory condition. This is a scenario I'd actually like to see, since it might put an effective end to the kind of fighting we've seen in the middle east.

Your argument is of course correct when we consider two countries which are both capable of producing such weapons and neither side has a nuclear weapon. Saudi-Arabia and Iran are candidates which could probably fall into this kind of an arms race and that would indeed make the situation there even worse.