I know you're coming from an enlightened place here - so if the best people were a mix of women and cultural minorities, with not a single middle-aged white man in view, you'd be fine with that.
That's admirable and in that respect I agree with you.
There's a "but" coming. Please bear with me a little as I try to elucidate my thoughts.
Firstly I think that a mix of differences in life experience is hugely important in any senior role, especially government. Just like you don't want all Labor politicians to be ex-trade union bosses, and you don't want all Liberal politicians to be ex-IPA, I would argue that EVEN if the "best" candidate (and what does that mean for government?) happened to be, in every electorate, a middle-aged white man, it would not be a good thing for the government to be compiled of them.
With the best will and intentions in the world, a group of men cannot make the best decisions regarding the welfare of women, for example. And the reverse is true. They simply do not have the lived experience of the gender to inform their decision-making. Something they consider a good policy, having considered its impact on the other gender, may in fact turn out to have a subtle component which is negative in the long term for the other gender. If there was someone of the other gender on the team they may pick up on it immediately and say "Hey - but what about..."
Obviously the same goes for gay/lesbian (not saying you have to have a transgender person in government - but at least someone who knows what it's like to be in that non-traditional bucket), immigrants, cultural background, religion (including lack of).
Secondly is visible representation.
Australia is a multicultural society. We say that, but I think for many people they still think of Australia as a mainly white "christian" country. According to Wikipedia, northern European accounts for between 55 and 70% (the 15% who put "Australian" in the ancestry census question are probably mostly white). So at least 1/3 of the population is ethnically diverse.
As for religion, as at 2021 "Christianity" was 44%, followed closely by "No religion" at 39%, then around 3% each for "Islam" and "Hinduism" and about 2.5 for "Buddhism". (I think I read somewhere that "No religion" had actually overtaken "Christianity" in a later census).
Now obviously it would be almost impossible for the government to be a true representation of every ethnicity, gender, sexual preference and religion. There are only so many seats in each house for a start.
But, I would argue that if 50% of the population (women) look at the major parties and saw 0 women in cabinet positions, they would probably think that politics is not a healthy place for ambitious women. Same for ethnicity/religion (and disability). If you see only white people in government, no hijabs (not including Pauline), no Jews, no Asian/Indian/Arab/Indigenous faces - then you would probably feel somewhere deep inside that you're not truly being represented.
The (relatively) recent same-sex marriage laws would probably not have happened if there weren't gay people in Parliament who initiated, pushed for or supported bills.
Of course you have internal fights and factional plotting. You mentioned Plibersek - pushed out because Albo doesn't like her (I think more likely, he correctly sees her as a threat). Same with the Libs. After a series of disastrous leaders (Abbott, Morrison, Dutton) they finally choose their first female leader who was probably the best of a bad lot, only to tear her down in 6 months and put up another useless twat whose biggest claim to fame was posting an applauding comment to his own Facebook page.
Anyway - the point is, I think there are subtle benefits to having a variety of personal attributes and backgrounds in leadership groups. Sorry it took such a long post to say this!