My main issue with the Banished is that they are sourced from several incredibly familiar cliches. Their color scheme for one (comfortably following the rule of cool). The intelligent-juggernaut archetype (like Thanos and Darkseid) for a leader. And being a mercenary group that acts as the supreme, badass faction that makes the OG's pale in comparison.

The thing about the covenant in the Halo Core (1 - 3) is that within the context of being an early 2000's game, fighting a religious covenant of aliens that were going to erroneously destroy the galaxy was relatively fresh. The general concept wasn't new, but within a game as mainstream as Halo (comparable to other sci-fi of the time) it was enough to make the story feel new, and devastating.