Looked at in a snapshot in time, it would be unrepresentative. After all, there are plenty of men and plenty of white people in this country. But are we trying to make the number of seats in an institution representative? Or are we trying to make the number of seat-years representative, i.e., integrate over the dimension of time as well as seats.
When you consider the temporal dimension, even a fully black Senate or all-woman Senate would be still fall far short of offering those demographics fair representation when optimizing for seat-years. It would take at least 50 years or so of domination by those demographics before things start to even out.
Personally, I find this framing helpful when considering what it means for public institutions to be representative, and why I am supportive of efforts to make it more so.