I don't think it was too harsh. Sure I don't know what point was off and all but the teachers are pro so I'm sure they know what they're talking about. They also said that Happiness was just barely okay. There is a huge difference between doing their own song and doing a song that any of the senior groups have done, which was all the teacher said. If you can't even do your own stuff that's sad, pretty much. In the first clip of them doing it, they danced with Ogawa and Taguchi, which I assume is because they were teaching the newbies how to do it - and the teacher then said that they weren't following/paying attention to what Taguchi had said/done while teaching them. Nothing bad with that either.
It is harsh sure, but they can't really sugarcoat anything because... they don't wanna hurt anyone's feelings or something. The teachers' job is to make sure the girls can put on a professional show - if they can't, they won't participate as much.