so, consider the following conversation:
「その日本酒、どう?」
「うん、わるくない。ちょっと甘い」
「本当?飲んでみる... げっ!全然甘くないよ!
「まあ、it's sweet, for sake
Essentially I'm trying to say that something is not sweet in absolute terms, but is sweet relative to other members of the indicated category. Other examples might be "It's slow for a motorbike" or "It's gentle, for a roller coaster."
The best I could come up with was 「ほかの日本酒と比べたら、あまい」which gets the meaning across, but feels a bit clunky to me.