The thing with Zukki's weight is that she most likely wants to be her former weight again, an idol has a much better time being as an idol when she is thin. No extra fabric on costumes, not being teased for being "fat" in particular. Sure, they get teased for plenty of reasons (see Momo), but I think it's much worse when you get teased for something that isn't part of your idol character. Maasa looked rather upset when she was called fat last year during that show where Momoko got hi-jump-kicked several times. On the other hand, the moment she got thin back in 2009 she got a photobook for the first time.
Zukki's weight isn't wrong and I doubt anyone is judging her because of that, but it's true that idols are supposed to be thinner. Personally, I like her a lot (definitely more than Haruna, actually).