I think there are two things. In nerdy political science terminology, we talk about symbolic representation and substantive representation, so there's a separating out about how we look from our ideas. For example, we often point to Thatcher. She was a woman, but obviously not great for women.
I would say that both are important. You want to have symbolic diversity, or the diversity in the way that we look, so that we can look at Parliament and think, “I should be there.” However, we also want to believe that people of all parties and all ideologies and all ideas can bring their ideas forward and have a chance as well. I think sometimes those two things match up and sometimes they don't, but they're both important.
I would say symbolic representation is not enough to ensure substantive representation, but also substantive representation is not such a big priority that we can sacrifice symbolic representation, if that makes sense.