CiG
Harbinger of Metal
That's exactly why it isn't useless, in fact. He's a major conservative voice in Hollywood, and he got there by exploiting a conservative streak in the demand for popular entertainment. You can't just say he doesn't count because he's too popular.
But aside from Eastwood, you have Michael Bay films, Peter Berg films, Paul Greengrass films (to name three directors) all of which draw tons of money and none of which care about being politically correct.
He was established well before the bias really took hold, so again, pointless. He was established before the 70's even came along. More credible examples would be recently established people, of which there aren't very many. Vince Vaughn didn't come out as a republican conservative until well after he was established.
It produces some of that, surely; but it also has plenty of room for right-leaning films and writers.
Any examples? Patricia Heaton actually noticed that she lost work right after she became publicly conservative. I don't really see a lot of examples supporting your refusal to accept this bias.