Are you sure you've been playing Civ? Just about ever Civ version in existence had wargamer strategies as the best performing strategies in both MP and SP(Deity or Sid level), except for maybe Civ I where the ridiculous score punishments on conquest victory meant you beat everyone down in combat, expanded like crazy and won an early space victory with only 1 or 2 opposing Civs left. I mean if its not supposed to be specifically focused on warfare stop making warfare the best and easiest way to win in every single version.
Well, this could either be by design, or through imperfect balance. I tend towards thinking it's the latter. I mean, it is a self-declared empire building and managing game. It makes sense for warfare to be one of the dominant, if not the dominant, strategic path in such a game. But that doesn't mean that the game is a warfare focused game. The focus is still on building and running an empire; the warfare is supplementary to this aim.