Even with game mode as slaughter, game ended when i killed citadel. i can see that as being inteneded, but on slaughter i'd prefer a type where their citadel didn't die and maybe their last defenses were stronger so the match would last longer. I chose slaughter so that the game kept going, not ended.
so if maybe the maps were changed to create a more fun slaughter type (dont allow enemy near citadel) or clarify in options that slaughter is more of a second way to win