As I understand,
1) setting an app as an accessibility option was the "old way" for a password manager to observe the foreground app to recognize login prompts but it came with a few downsides, one of which being that the password manager would constantly poll for login prompts, it affects lockscreen security or something, and it is a general security risk as an app can observe other apps.
2) The new Autofill service feature offered in Oreo to address the performance issues of accesibility access.
Other random things 1Password doesn't use but I've seen in other pw managers:
3) Display over other apps allows the app to overlay other apps (messengers use this for chathead features. Lastpass uses this pre-Oreo to pop up credentials to copy/paste into logins and also a password bubble thingy.)
4) Apps with Usage access. Well, I don't know why Lastpass has this unless it's one of their analytic libraries they include or if it does indeed help with observing the active application.
5) Modify System Settings. This is a goofy one. I think it's so an app can toggle wifi and bluetooth amonst other things. Google really doesn't clarify why many apps declare this and a lot of obscure apps try to.
I guess my question is, with Oreo, can I simply register 1Password as an autofill service so it doesn't affect performance? As I understand, setting it as an accessibility service just allows 1Password to detect webpage logins if you use Chrome-based browsers. If I use Firefox for Android I wouldn't think it applies, right?