As someone who has purchased Facebook ads, it's /so very evident/ that this is happening, that it's not particularly hard to compile evidence.

Here's a specific example: we ran around $1k in ads last year, targeting senior-level engineers at technology companies, but the ads were getting liked by mostly people who worked minimum-wage jobs. Twitter and LinkedIn targeting were fine with pretty much the same parameters.

This is one example, obviously, but it's so trivial to see that targeting is almost completely uncorrelated with reality, that it's not hard to come up with more examples.