Consider "I looked around me, and saw only empty space"; "I shouted and listened for an echo, but heard only silence"; "through one door I saw the familiar outside world; through the other, only the emptiness of space". "Nothingness" isn't quite the same as "nothing"; it means something more like "the appearance of nothing where you might have expected there to be something". (Perhaps that's why I thought inanitas (literally "emptiness") rather than nihilitas, but another reason is that I simply didn't think of nihilitas :-).)

If nec and neque are semantically equivalent, then I agree with you in preferring nec defensori and neque victori on metrical grounds. If soter is acceptable Latin for saviour/rescuer, and if its (dubious) ablative is something like soteri -- neither of which I'd be too sure of! -- then "non est soteri soter. nec defensori dominus" is an improvement rhythmically. I think. I was never any good with Latin poetry.