This is incorrect in Season 3 regardless of what you read indicates. In Season 3 of The War Within, the maximum number of Sanity Loss you can obtain from Malefic Core caps at 80% per run, and these come from the following items only:
Malefic Core
It’s been like this since the start of the season, however I don’t recall Blizzard specifically explaining these changes or announcing that they were coming in Season 3.
Edit: the information you’re referencing in your first post is the way it used to work, but that isn’t the way it works now.