Peer review isn't perfect, but it's the best system we have for quality control.

I don't think that's true. Journals were invented to solve a problem that largely does not exist any more. Before journals, scientists communicated by letters, which were not available to anyone outside the small, scientific circle. Journals allowed communication of results to a wide audience.

The problem we have now is ensuring quality. Peer review was not designed for an era of interactive communication. Lots of better systems could be, and should be devised. Reddit is actually a model of a better approach.

More often than not, the current system of academic publishing interferes with scholarship, rather than furthers it (and I say that as someone who has both published in peer reviewed journals and reviewed for them). There are many rent-seekers in the process, so it is often expensive. It is also tremendously slow, and dialogue between competing views is rarely encouraged (and sometimes actively discouraged). Readers who are not familiar with the literature have very little to go on to gauge the acceptance of a given paper within the community of experts (citation indices are a mediocre approach at best).

Lots of publishers are for-profit, leading to competing interests. Some have created fake journals for well-financed interests to use as advertising. Even the ethical journals will often decline to publish failures to replicate findings, negative results, or other "low citation potential" papers.

Have you ever bought a textbook and wondered why the price was so high? It is an aspect of the same problem faced in all academic publishing. Journals are treated as profit centers. Rather than being circulated, publishing houses know they can charge thousands of dollars for a subscription, and academics will have little option but to pay. They add virtually nothing (often the editor and peer reviewers are volunteers) and charge enormous amounts.

So when it comes to light that even the benefit that publication in a journal might manifestly add over putting the article on my website or arXiv is often minimal, I wonder why we don't improve the system.

Academia needs a better system.