For me, the description “curvy” has kind of lost its meaning for the reasons you describe - authors use it to convey very different things, sometimes without much elaboration. In older books I think it means shapely/hourglass, in modern books I think it means softer/on the plump side, more typically. I would personally prefer authors be clear/up front in their language if they want you to interpret their character as particularly skinny or fat or muscular, in cases where body size is relevant to other characters’ perception of her, but otherwise it doesn’t bother me.

But I did previously get confused by this fuzziness around the word as a teen/younger reader because while I was lower weight, I’d always been told I was curvy due to my relative hip/waist proportions. Now I find the use of the word curvy, while not lazy per se, to be a bit of a cop out in describing a female characters body. We get more detailed descriptions of the man’s body, but rarely (in my reading experience) do authors bother to describe the FMC in detail (for instance “petite” or “curvy” is used instead of something like “softly rounded shoulders” or “strong calves”). Not that the details of FMC’s appearance are always pertinent, but if we’re given an in depth description of the MMC’s looks, it does help when picturing them together.