In “The Masque of the Red Death” there are several types of conflicts that represent larger ideas.
Of the examples you gave, I think that power versus powerlessness is the best fit. The people are powerless, and the Prince is powerful, when it comes to the pestilence. However, when it comes to Death, the Prince and his followers are powerless, and only Death is powerful.
First of all, there is a character vs. nature conflict: the people versus the Red Death. This conflict does represent the larger idea of impending destruction caused by lack of intelligence or action.
There is also the character vs. character conflict with Death, because Death is a character in the story. The symbolic struggle with Death represents the larger idea that ultimately, all living things are in conflict with death as it tries to claim them and they try to escape.
Finally, the outlandish masquerade ball creates a character vs. character or character vs. society conflict between Prince Prospero and his poor, suffering people. This conflict symbolizes the arrogant detachment of the wealthy, as they spend lavishly and condemn their less fortunate fellow humans to death.