Firstly, if they were trying to introduce those concepts to the player, then they were doing a fairly poor job of it.
They never introduced the Brotherhood to new players, they introduced goody-two shoes wasteland knights, with no real motives, nonsensical goals, and a complete disregard for what the Brotherhood was originally about.
They never introduced Supermutants, they introduced big, dumb orks who shoot everything on sight because reasons.
Secondly, if the point of Fallout 3 was to bring console players in to the lore of the franchise, then what's the point of rehashing the same old bullshit in Fallout 4?, There was absolutely no need to have Supermutants in Fallout 4, they contributed nothing to the story or universe, and the game could very easily exist without them.