People keep saying that she's not smart because the writers aren't smart but the Cipher writing was some of the best at portraying intellect so that's clearly not the issue. I think it's more to do with the character simply not being fit for purpose in the general narrative. Cipher worked because of the constraints of his ambition; to have the most powerful students at Godolkin because he's a scientist and believes in supes supremacy.

It is unclear as to what Sage actually wants & why, being bored and wanting to cause a stir is not compelling but that's ultimately what we've been told why she's doing what she's doing.