Excerpt:
Most major subreddits show a decrease of between 50 and 90 percent in average daily posts and comments, when compared to a year ago. This suggests the problem is way fewer users, not the same number of users browsing less. The huge and universal dropoff also suggests that people left, either because of the changes or the protests, and they aren’t coming back.
If I recall correctly (I might be wrong), July/11 was when the 3PAs stopped working. Regardless of that I don't think that those karma farms relied on the API, because as @PoliticalAgitator said they want to avoid shadowbanning.
However, if we follow your reasoning, it's still a fucking dumb move from Reddit Inc. to kill what made the place active. The issue with bots was never their usage, but rather that they went unmarked, pretending to be human beings [re]posting stuff.