I understand the fight your picking, but really this isn't that much of an argument. "Mainstream media" makes mistakes. It has perspectives that leak through into interpretation. It has blindspots in coverage. But mainstream journalists almost to a fault genuinely view their job as bringing important facts to their audience, and they care about getting things right. That's just not true of the partisan press on the right, and you know it as well as I do. Let's actually measure:
Here are the biggest three headlines I see at nytimes.com right now:
"West's Resolve to Block Russia Grows Amid Fears of a Protracted War"
"Likelihood of Trump Indictment in Manhattan Fades as Grand Jury Wraps Up"
"Piles of Garbage, No Showers: What Lockdown in China Looks Like"
All seem eminently plausible, reasonably descriptive of the content in the article, and (except arguably the China article) not written from an argumentative perspective. I'd happily read any three of these articles and "trust" their content (I did read the Ukraine one).
Here are the three biggest headlines at foxnews.com, fetched within a few seconds of the list above:
"President Biden's close relationship with Hunter associate who led company with China ties exposed"
"Liberals lose it after Elon Musk's tweets about the Democratic Party"
"GOP rep grills Biden's secretary of state over Ukraine 'lies'"
Every single one is written from a decidedly partisan perspective. One contains a value judgement ("lose it"), one uses deceptive quotes to be able to call something a "lie" without evidence (someone else called it a lie, Fox technically didn't), the other is a guilt by association fallacy.
I don't trust a single one of those things to give me the whole story, and I'd be shocked if even partisan republicans did. If I want to know what's "really" happening on any of those issues I know a-priori that I need to find more sources, because this one isn't giving me the whole truth. Giving you the whole truth, essentially, isn't what Fox views as its "job" in the same way that the Times does.