So their argument is that the tests are not providing causal inference, because the platforms can target the two A/B test groups differently.

With that in mind, my reading of this is: if you're a researcher trying to say "Advertisement A is more appealing than Y", you need causal inference and these tests won't give them to you. If you're a marketer just trying to determine what ad spend is more efficient, you don't need that causal inference.

In other words, they are debunking using these tools for research studies, and not as marketing tools.