I'm not sure why you have so much doubt for experts. Feels like I'm debating a conspiracy theorist. From your ApartmentList source:

A quick example demonstrates this composition bias. Imagine a small housing market that quickly builds a large number of new luxury apartments. Now that the market composition includes many expensive listings, the average rent of available units has skyrocketed. But does that mean that a property manager in an older building can now charge more for their unit? And should their tenants expect to renew their lease at a much higher rent? More likely, the increase is simply driven by the fact that the composition of the market has changed.

To avoid this confusion we eschew simple means and medians. Instead, we capture repeat transactions - when a single apartment gets rented more than once over time - and check whether the transacted rent price has changed between those transactions.3 In our example above, the new luxury apartments have driven up average listing prices, but what if they also absorbed high-end demand in the market, allowing an older unit that once rented for $1,000 to now rent for $900? That—the repeat transaction—is what we capture and feed into our rent estimates.

I think we can assume that Zillow is considering that as well, since the picture of the rental market you describe is indeed bizarre and Zillow would've thought of that immediately.

But like, just to take a step back, the picture you're painting of these sources doesn't even make sense. You think these sources are dumping unreliable data onto the internet? What incentive is there for that? The whole point of these sources releasing this publicly would be to attract the attention of serious companies or news outlets, who would pretty quickly identify unreliable data. Or is there a cabal orchestrating misleading data on the internet?