This is spot on, I think.

We should assess the properties of the current political system as emergent, not as some sort of top-down planned thing.

Life in Britain if you've got a decent salary and disposable income, have a stable marriage/family, have a stable job, have a mortgage or outright own a property, and have citizenship is pretty sweet. Meaningful political change for people in this situation might have a theoretical upside, at least in the abstract (you might want a fairer society, less poverty, less unemployment because you're a decent person and care about others) but it has a very personal, practical and massive potential downside.

Change for these people is indeed very risky. I don't have figures, but my impression is that a large slice of the regularly voting population are in more or less this situation. They might want laws or policies in one or two of the areas changed or tweaked, but not enough that they'd risk stability in the other areas. Besides, the main parties' policies are generally so averaged over what their votership want in the aggregate, that their manifesto matching precisely the tweaks you want (which bear in mind somebody else won't want, because it'll impact them negatively) is nigh on impossible, statistically speaking.

So, you end up with a stable political institution where change is disincentivised, and where the status quo has evolved its own culture and structure over decades, centuries even. That culture is that our 'elites', via a wonderful private education, the encouragement of parents, teachers, and other mentors, connections etc, end up in the profession of politics and end up doing quite well in it, because they've been trained and shaped for it pretty much their whole lives. It's the same reason why top software people were once 10 year old kids fiddling with computers and games and hacking in their bedroom. The current political elites probably at least had the concept and ideas of politics and leadership and power in mind at that age, even if they weren't actively being trained towards it at that young age.

Anyway my analysis is obviously very naive and a full one could fill several books, but regardless of the reasons, we shouldn't be surprised to see patterns emerge in a very stable system which resists change in the short term. The pattern in this case being that 'elites' rise to the top of the current system. We also shouldn't be surprised to see people accept this system, even despite its flaws, when it results in a pretty great quality of life for them, personally. Remember that the people worst affected by the things wrong with the political system are also those least likely to, or unable to, vote. This too is an emergent property of the system and is just a mathematical inevitability, however unfair it appears to be. If suddenly the tables flipped and everyone who previously voted stopped, and everyone who never voted started, the system too would flip on its head within the space of one or two election cycles. But that will obviously never happen.

It's true that every system we have was just invented by humans, nothing is written in stone and we don't have to run society the way we do. However it's also true that (assuming actual democracy exists) political systems generally emerge and then stabilise from the aggregate of what most people truly want. The problem with aggregates over populations is that they're incredibly difficult to change and can result in undesirable artefacts, but these are generally artefacts that are just palatable enough that they can just be ignored. Such as elites always being at the top of a government (regardless of party) that provides a stable, good life for most of the people that tend to vote.