No one is saying that there isn't an optimal weight for pairs skaters. Of course there is. But once again, there is no evidence that Julianne was "overweight" to the point that Charlie couldn't lift her. Regardless, her coach forced her to stay within an unrealistic and apparently unscientific weight range for ten years. And as the story says, when she did have trouble maintaining that unrealistic weight, it was because she was too nauseous from skating-related concussions to train full out.
This isn't the first time that someone has posted a news story about a female pairs skater in an abusive and unhealthy training situation, and some responses have been essentially "well, pairs skaters can't weigh too much". No wonder it's so hard to make meaningful change in this sport.