I have all the same issues and frustrations you do JONS - thank you for the excellent summary. With the change to identical pricing to 1Password and the expiration of my previous $12/year membership I am planning on doing the same switch to 1Password since for $36/year I might as well get a password manager that works with Safari.
From what I understand you're right about 1Password actually originating as a MacOS application. I believe it also supports TouchID for unlocking, so there's that bonus. And regarding autofill, yes I believe they view that as a serious security risk to have it enabled so it's not an option at all. I would be curious if you knew if there are any keyboard shortcuts that can be used to manually select/fill a matching site; this was my workflow with LastPass before I started using Safari; in Chrome I had autofill disabled but would just use shortcuts like Ctrl-N or Ctrl-P to cycle through the next or previous matching site. But apparently with autofill dead with LP on safari that means shortcuts are dead (I suspect because they're just triggering autofill of the next/previous site, and autofill doesn't work so nothing happens).
LP just released version 4.32.0, which, thankfully, seems have made significant progress in addressing the major issues I was experiencing. Form fill is now working properly for me, and most sites display the correct login credentials. I did encounter an incidence yesterday where credentials from the previous site were displayed, but so far that's the only time thats happened for me since updating to 4.32.0. Additionally, i have multiple login credentials for the particular site, so that might have been the cause.
Update to 4.32.0 and see how you go.