Have you ever seen the videos where anchors across the country read the same lame joke to lead into a national story? Do you know who writes those stories? CNN. So of all the companies to complain, the one that pre-writes jokes and headlines for their anchors is not the one that carries a lot of weight.
Sinclair is advertising, trying to get a leg up on its competitors. It's called an image campaign and it's been done for decades; yes, anchors are regularly involved in cutting the promos. There is literally nothing out of the ordinary here.