I also find it staggeringly ridiculous a narrative of having the Shivans being scared of the GTVA and "folding" the hand, when all the tactical signs point to the simple fact that these species simply have no hand against them. It would also paint them as absolute cowards, I mean come on.
The very point of having the Shivans' objective be towards the Capella star and not against the Terrans / Vasudans is made precisely to avoid the contradiction of having an unbeatable species being "beaten" by the GTVA at the end of the game, or alternatively, have the GTVA being absolutely demolished by them (not good for the gamer morale... a contradiction that Mass Effect failed to solve I'd say).
Thus they were written like the aliens in Rama, or any other Lovecraftian species, wherein we are only saved because we were not in their target. The giant mammoth steps on some of us (ants) but the "ant colony" is saved because the mammoth is just interested in going towards the lake to drink some water. This is the only kind of narrative that is able to "save" the humans while allowing the Shivans all their might, all their terror and all their alien nature.
From a pscyhological point of view, this is the arc of a brash teenager meeting a really tough challenge from Nature, ever becoming greater in peril, but always confident he will be able to achieve success, then a harsh realization that such challenge is waaay over his head, that Nature is waaay more cruel and tough than the brat could even dream of, and then be saved by mere contingency, out of his control. A lesson of adulthood, if there is one.