Redfin/Trulia/Zillow I would assume make more money on sellers than buyers (listing fees).

Right now inventory is extremely low even though prices are high, because everyone was told that prices would crash as interest rates rose, so prices basically didn't go down at all or even continued to increase. I suppose Redfin is financially interested in reminding sellers that prices are actually just as high this year as they were last year.

Do they take direct listings? I assumed they got all their data from public information aggregators and MLSes. You can even see MLS watermarks in some photos.

They do, although most listings are from an MLS.

I think they might also offer some kind of paid/pro tools for individual owner-sellers and agents who might want to use them.

They also do business on the buyer side too, where they connect you with local buying agents (in a kind of misleading way, making you think you're booking an offer) and presumably impose some kind of commission for that.

And who knows who they're selling aggregated user data to.

Both? I can imagine someone looking at the graph showing a decrease of affordable homes sold over time and wondering if they will soon be on the other side of the line.

It’s a big leap from “I can imagine someone” to “this demonstrates a meaningful financial incentive that colors the content”

It's a very small leap from "Redfin posted something on the internet" to "There is a financial incentive to this activity"

Of course that’s true. The question is whether its actual incentive is anything like the one you’ve surmised and used in your critique. I think that your take seems strained and that the actual incentive is likely more sophisticated in general and intuitively biases in the opposite direction if in any relation to your point at all.