HaLeivi:
As far as the umos not keeping their oath making any difference regarding us keeping our oaths, there is nothing to argue; it is nonsense.
The purpose of the oaths is to keep the Jewish people alive in galus. Regardless of what the goyim do, we need those oaths for our own protection in galus.
The Rambam, in Igeres Teiman, told them that even though they were heavily oppressed, they were still bound by the oaths.
GAW:
Deos Kozvos, even heresy, do not necessarily invalidate the believer himself.