But again... to get anywhere, you would have to assume they think like humans do and not only that, you would have to assume that they pretty much think like contemporary american/western nations think about warfare.
(Even in historic and contemporary human societies/thinking you will find instances where certain concepts and codes of behavior take precedence over mere military "efficiency". Nope, none that i know of would apply to the Shivans, but it certainly demonstrates just how limited a viewpoint focusing on military efficiency really is)
And you just have to take a look at General Battutas suggestion above once more and you already have at least one possible explanation that would make "human" thinking outright irrelevant.
What would a human cell or antibody "care" about sacrificing itself ? Why do we assume that 80 Sathanas were all that the Shivans had anyways ? Because the GTVA assumed the Lucifer was all they had after FS1 ?
In any case "Expenditures of resources" really only means anything within a very tight corsett of thinking and necessarily doesn't even have to mean anything even for humans. For all we know... the Shivans attribute as much "value" to 80 Sathani as we attribute to the water that we flush down the toilet every day. If they even have a concept of "value" to begin with.
If anything, then everything we learned from the previous games is that the GTVA did appear as some sort of irritanct (likely through entering subspace) and therefore the Shivans marshalled some forces against it, but didn t take all that seriously and i severely doubt that it's a matter of "winning" but rather seeing if a threath/irritant can be dealt with - with whatever force has been dispatched... and if not, well ... if it keeps being an irritant, then it will eventually warrant more "attention".
In any case... something along the lines of an "organism" analogy strikes me as much more intriguing. That would make the GTVA a sort of virus or bacterium dealing with an immune response and the irony of trying to defeat such a response "once and for all" would naturally be quite priceless, even if its propably overextending the analogy way too much already. But at least something along these lines would at least offer a somewhat satisfying "scope" that would mesh well with the spirit of the previous games and that the traditional sci-fi cliche of portraying a specific selection of human traits as "alien" merely by exaggerating them couldn't hope to match.
I.e. the Star Trek way: Emphasize human aggressiveness and honor = voila, Klingons. Emphasize rational thought and logic = tada Vulcans! Greed = Ferengi.... et cetera. Cardassians ... propably Nazis lol.
Along similar lines i would find ANY kind of explanation portraying Shivans merely as an "older" race with advances capabilities and/or a "different agenda" that happens to oppose whatever the GTVA is doing as extremely disappointing and unoriginal... and whatever "fluff" like "artifical creation/robots" or "hivemind" goes along with it really doesn't matter either, as long as you don't escape the underlaying cliche.
It all boils down to saying "Well they are kinda like us, but different."
I would argue that any kind of explanation that would be even remotely satisfying would have to start along the lines of "They are nothing like us". That's the real beauty of how
designed them and should be respected
But as said before... even a "perfect" explanation would be futile as long as it isn't "official". So while one can discuss the merits and flaws of different solutions, it's really all a quite moot point.