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.
Well, the site says it shouldn’t be used for serious purposes, but I would say it’s still safe to consider it semi-quantitative. If you see a drop like that, there really is a drop. What the exact value was before or after might not be that reliable, but it’s not even important in this case.