Sir Ackbar of the Night's Watch watches Season 7

Is it ever explained why Witchy Woman told him all of those things? Was she lying? Did she really believe them? What was the point of it all?

This is why I begun to assume that Stannis's subplot was just an elaborate way to set her up for the later seasons, because if she doesn't play a larger role now then I guess I don't see the point of her in the first place. Something similar happened with the Tyrells. They were supporting characters in the subplot with Remly, then were propelled into a larger role when Stannis killed Remly. That justified that whole subplot's existence. Remly ultimately wasn't important at all, but Margery and her brother were. Perhaps that happens with Davos and the Scarlet Witch?

Stannis' arc was a thematically rich one, the descent of a power hungry man into darkness. It is fitting that his quest ended in early defeat. I just expected either a grander finale for him or a new story arc for him after his defeat.