Mhairi Black, the SNP MP and deputy leader of the SNP’s Westminster group, landed one of the year’s best Prime Minister’s Questions lines on Wednesday last week.

The day after she announced her intention to step down at the next General Election, the Deputy Prime Minister, Oliver Dowden, noted that he and Ms Black had been part of the same intake in 2015. Ms Black responded that she was “pretty sure we’ll be leaving at the same time as well”.

Watching that performance, you could have been forgiven for thinking she felt freed by her announcement that she would be standing down. She looked and sounded at home exchanging barbs across the Commons floor.

But it was the institution of Westminster, in which Ms Black has made a name for herself as one of the SNP’s best and brightest and as one of British politics’ rising stars, that she blamed for her decision to stand down.

She cited its anachronistic processes, boorish culture and overall toxicity as the key determinants of that decision.

She pointed to the endless nights of divisions and the colleagues she had witnessed being bullied and, on occasion, physically dragged into the ‘right’ lobby by party whips.

She noted that Westminster is “one of the most unhealthy workplaces you could ever be in”, discussing the extent to which unacceptable behaviour is tolerated and the poisonous atmosphere that creates.

Ultimately, she says she was standing down because she is “tired” of politics at Westminster.

Naturally, Ms Black’s opponents have found many reasons for her to step down that have nothing to do with her expressed justification. Foremost among these is that her seat, or its successor under the proposed new constituency boundaries, risks flipping to Labour at the next election.

Others have called her a hypocrite for characterising politics as toxic, arguing that she herself has contributed to that toxicity.

Personally, I don’t find her decision to stand down or her reasons for doing so surprising. She has been making these points about Westminster for many years, and it’s no surprise that someone who has spent almost a decade in that place, tolerating that toxicity while finding themselves in perpetual, ineffectual opposition, would eventually throw their hands up and call it a day.

I also take exception to some of the language used to describe Ms Black in the days following her announcement. She and I went to the same school in the south of Glasgow and were in the same graduating class at Glasgow University. While I cannot claim to know her well, in my experience she is an empathetic, intelligent, talented person – and her colleagues in London will miss her.

But set all of that aside. Regardless of what you think of Ms Black, her politics, or her motivations, she is right about Westminster. And while I understand why her announcement is being framed the way it is, there is little value for our politics in trying to decipher her true motivations by reading the tea leaves.

On the other hand, there may be something to be gained from discussing the state of Westminster politics, which, I would argue, is in a worse place than even Ms Black articulated.

Is Westminster anachronistic? Undoubtedly. From the divisions Ms Black mentioned to its arcane linguistic traditions and the political pantomime of the legislative back-and-forth between Commons and Lords, it is an institution out of its proper time in the mid-19th century.

Is Westminster sexist? Inarguably. Research for the Fawcett Society found that seven-in-ten female MPs have witnessed or experienced sexist behaviour at Westminster – a figure made very easy to believe by repeated rows over MPs’ rights to, for example, maternity leave.

Is Westminster toxic? Ask the alleged victims of the dozens of MPs accused of sexual assault, misconduct, and bullying behaviour in recent years. It is a workplace where staff have to effectively brief new arrivals on which MPs to avoid, who are likely to make sexual advances, or might get ‘handsy’ after a few drinks in one of Westminster’s many on-site, subsidised bars.

This is an institution many of whose members think it is justified to take to the airwaves and social media to whip up hatred against colleagues for holding the government accountable. The fact that members of the Privileges Committee had to arrange extra security while investigating Boris Johnson over his lies to Parliament should single-handedly settle the question of Westminster’s toxicity.

And ultimately, it is an institution that no longer works for the people MPs are sent there to represent, if it ever did. A minority of the electorate gets to choose a majority of MPs, who are then kept in line by hook or by crook by a small minority of senior MPs wielding the power of patronage and punishment.

As a result, it delivered austerity followed by the hardest of Brexits without majority public support for either. It’s no wonder that polling repeatedly shows that the public feel unrepresented at Westminster and feel they have little or no power to influence the decisions made there.

Westminster is a sclerotic and dysfunctional institution at best that is, quite literally, crumbling. Without serious reform, it may take the country with it.

So, it’s no surprise that Ms Black has concluded that Westminster is no place from which a young politician, keen to improve the lives of their constituents, can achieve anything of value.

Say what you will about Ms Black’s politics, motivations, or character. She is right about Westminster and, in her announcement last week, if anything went easy on it. It is long overdue radical reform, reform I fear will not be forthcoming regardless of who is in government after the next election, given how cool Keir Starmer appears to be on the constitutional reforms he commissioned Gordon Brown to produce.

Instead, we will continue to languish under an unresponsive, poisonous institution out of time, unfit to govern a 21st-century society. No wonder Mhairi Black is standing down; the real question is why she persevered this long in the first place.