I haven't done guild tasks since 1.18, so I can't say whether they were nerfed. But before 1.18, they offered SP. If I remember correctly, it was 300 or 500 SP, depending on level of the task.

Pro tip -- Guild Tasks offer SP for whatever class you are when you turn it in for a reward. So if you turn in the undyed cotton cloth, and you've got your Armorer tool equipped, you get SP for Armorer. (At least that's how it was before 1.18)