Mainstream != serious. In fact it's quite the opposite, as serious news organizations cannot match the output of mainstream news. Even one story per month is a success for many.
In serious news organizations, there's quite a few steps between a journalist writing a draft and that draft being published. Fact-checking is one of them, having a competent "boss" (called an editor) is another.
Most news orgs have both a "serious" department and a "publish as much as possible" department, with far different requirements. In general, if you're publishing something along the lines of "X said Y", you don't need a rigorous process. If you're doing an investigation in which you're accusing someone of doing something illegal, then you need a far more rigorous process, otherwise you'd be sued out of existence pretty quickly.
Of course, having a rigorous process doesn't mean you won't get sued at all, but there's a term for that: SLAPP (strategic lawsuit against public participation). In those lawsuits, the goal is not to prove the story wrong, but to just waste news org's resources on defending their reporting in front of a judge instead of doing their job.
I'll use a non-American example. Such outlets present themselves as more serious than they are, particularly the BBC. The BBC presents itself as neutral, for example, when it is no such thing in many areas. When it comes to British foreign policy or the Royal Family, its biases are clear. The BBC tried to bury the Prince Andrew story repeatedly.
I pointed out to someone that the BBC was institutionally biased against Scottish independence, just by the nature of its funding. The BBC is funded by the TV licence, and if Scotland became independent, then the BBC would immediately lose 10% of its potential funding.
Other media outlets are the same. The question is who owns them, and how are they funded. State broadcasters have to kowtow to governments, or they can face trouble (as happened in Israel a few years ago when Netanyahu shut theirs down). Ones owned by major media conglomerates and corporations will reflect the interests of their owners. We have seen unions play less and less of a role in the political arena, probably partly because large profit-making corporations don't want them to be publicised.
I don't know how any of that has anything to do with what I explained to you. Two completely separate topics, I'm not here to indulge your every gripe you have with news.
> State broadcasters have to kowtow to governments, or they can face trouble
Very good example, BBC has criticised the government many times, and even did embarrassing investigations and fought in courts to get to publish them. A very good one is them fighting like hell to publish that MI5 are shielding an informant who is a pedophile. And they got to publish it, and directly say that MI5 tried to stop them via the courts on the grounds of "national security", but the courts disagreed.
So yeah, no.
> Ones owned by major media conglomerates and corporations will reflect the interests of their owners
Depends. Le Monde is a French left-wing newspaper (top 2 in France alongside the right-wing Le Figaro), which is majority owned by a holding company majority owned by one of France's premier tech billionaires (Xavier Niel). But everything is structured in such a way that he barely has any control (he can't even sell the holding company without approval from the remaining owner of Le Monde, a representative body of the journalists, staff and even readers). It has full editorial freedom.
In serious news organizations, there's quite a few steps between a journalist writing a draft and that draft being published. Fact-checking is one of them, having a competent "boss" (called an editor) is another.
Most news orgs have both a "serious" department and a "publish as much as possible" department, with far different requirements. In general, if you're publishing something along the lines of "X said Y", you don't need a rigorous process. If you're doing an investigation in which you're accusing someone of doing something illegal, then you need a far more rigorous process, otherwise you'd be sued out of existence pretty quickly.
Of course, having a rigorous process doesn't mean you won't get sued at all, but there's a term for that: SLAPP (strategic lawsuit against public participation). In those lawsuits, the goal is not to prove the story wrong, but to just waste news org's resources on defending their reporting in front of a judge instead of doing their job.