I think you're right, but with an asterisk of sorts. I definitely believe that historically the "mainstream media" (by which I mean outlets like CBS, ABC, NBC, NYT, WaPo, NPR, etc.) has had a significantly more liberal lean than conservative. I think it's for a lot of the same reasons that academia has historically had a more liberal lean than conservative, which is to say, that conservatives have largely eschewed going into the field of journalism altogether. I don't think that there was ever some Illumniati-esque meeting of the media minds where it was decided that mainstream media outlets would lean liberal versus conservative; I think a lot of it was self-selection, as I mentioned. In other words, I don't think that the mainstream media became liberal in the aggregate out of spite for conservatives or for nefarious reasons (to borrow a phrase from Michael Jordan: "conservatives buy newspapers, too"). I think it happened naturally as a result of the self-selection I mentioned, and then continued to perpetuate itself for decades.
Something that I think that conservatives have done, though, as a result of the mainstream media having a liberal bend, is absolutely kick the left's ass when it comes to creating and sustaining an entire media ecosystem dedicated to propping up the conservative party. CNN and MSNBC are child's play, IMO, compared to Fox- and by that I mean their reach and influence. (That's not to say that they aren't liberal-biased; they are. I just mean that they aren't nearly as effective at message-shaping and agenda-setting as is Fox).
So while the mainstream media is definitely liberal-biased, the right wing media ecosystem that started with Fox and has since spawned off countless podcasters, social media personalities, influencers, etc. is extraordinarily more successful at crafting and disseminating unified messaging that benefits the conservative party, than the mainstream media is at doing the same for the liberal party. I absolutely hate most of the right wing media ecosystem for its propensity for lying and grifting, but I am both envious and in awe of its effectiveness. It's something for which the left has had no match historically, currently has no match, and will likely never have a match- to the detriment of the Democratic Party. So while the historic norm has been that the mainstream media has been significantly biased in favor of liberals, I think that their effectiveness in crafting and disseminating messaging that favors the Democrats is at an all-time low compared to that of Fox & Co. And I think it's going to continue to cost Democrats dearly at election time.
