one new hero will hardly change up gameplay...
assuming theyre only releasing one, which is what it seems like
one new map will change up gameplay even less, considering you will only see it a 13th of the matches you play. I admit a new game mode would be the most "game changing", but even then, if it's only one map at launch that's still only a 13th of a chance to even play it, with a 5th of the time if it's a full 3 maps like the other modes. And you also have to think, if they added a new game mode, how unique would it likely be?