I don't have real data, but anecdotally this "feels" accurate to me. (Very long-time /. reader so I've seen the ups and downs.)
I would say total story comment counts were quite low from autumn 2015 through winter 2016 but have risen this spring.
Easy to compare "today" (meaning each day) to prior years using the old side-bar widget that showed past high-comment stories on the same day. Recent years are dramatically lower than past years, but the trend appears to be going back up.
Perhaps some researchers could get a dump of stories with comment counts, then chart them? (It should be possible to scrape if someone had the time.) Easy to see seasonality like northern hemisphere summer vacations for students.