Here's an article by Frank Tipler, Professor of Mathematical Physics, Tulane University, that explores this very question: "Refereed Journals: Do They Insure Quality or Enforce Orthodoxy?
IIRC, your observation that Einstein's work largely did not see the light of day in the professionial journals of his day is correct. But then, according to his great biographer, Abraham Pais, Einstein didn't bother to read them anyway.
I gather that Einstein unlike his close friend Niels Bohr was a bit of a "loner." He followed his own ideas, and didn't bother much about what other people were doing with the exception of Max Planck (and Bohr, of course), whom he greatly admired, and who motivated Einstein's discovery of the photon (1905).
Planck did get published in professional journals (and Bohr, too, of course). But this was before WWII, when (according to Tipler) new ideas could find a forum in such journals. (Tipler alleges that post-WWII, this doesn't happen much.)
Anyhoot, I encourage people to read the article at the link above, and draw their own conclusions.
I have a "funny story" to tell from real life, involving "my friend the astrophysicist." He submitted a paper describing how he derived algorithmic complexity measures of biological systems to the Journal of Theoretical Biology. It was straightaway rejected. (I saw the rejection letter. I didn't know whether to laugh or to cry. Basically, it just said "we don't do that sort of thing over here." )
But that is not the end of my story. The very person who signed the rejection letter, who shall be nameless here, found out that AG was contributing that article to an anthology edited by Joseph Seckbach & Richard Gordon (mentioned above in this thread). Since the rules of this excellent book permitted people to come and "rebut" any article included there, this same person showed up to "rebut" AG's article. Sheesh! This guy was following my friend around! A 25-page "dialogue" ensued between them, right after AG's article. Obviously, the motive was to "enforce orthodoxy."
But I think my friend whupped him big time. :^) The "gun-slinger" from JourTheolBiol seemed a littled "chasened" in the end....
Ha! I thought AG mopped the floor with him. But that's just my opinion, of course.
Thank you so much for sharing your insights, dearest sister in Christ!