I will say as someone with a limited visual field, toasts are very frustrating as they're almost always out of my field of view. Please keep indicators/notifications close to the thing that caused it.
Saving, when instant, does not need to notify the user. Not every action needs to notify the user.
As seen in the article, do we need a notification following a click to every checkbox? In most cases, the user should assume that the action is completed the moment it's taken. If not, you can add an inline loader and show a regular, maybe modal error if it happens.
"Save" actions, with the exceptions of large data, does not need further UI. Particularly the circle should be seen as a marker of the current state, not as a way to tell whether your action has completed successfully, so you shouldn't view it as a "10x more subtle notification"
Do you have a video or screenshot of this? I don't daily drive a mac so I'm having trouble recalling (I also am not sure what you mean by saving a document, in which context?). But regardless, I don't think a toast would serve me better there, that doesn't mean that ux doesn't suck either :)
