"Those war plans rested on a belief in the ineluctable superiority of the offense over the defense" (Jack Beatty).--The American Heritage Dictionary
One dictionary I consulted (allwords.com, as I recall) marked ineluctable as "especially literary, formal." I agree that the word is more likely to be read in a book than heard at a construction site.
But "ineluctably," especially spoken with energy and optimism, is so much fun: it invites hand jestures that register flowing forward movement:"She loves you. If you ask her to marry you, she will ineluctably say yes!" Furthermore, an echo of that magical word "lucky" rings within. I don't hesitate to promote ineluctable as a word worthy of comfortable place in the ambit of spoken American English.--B'n J'n