It would be premature to relate these numbers to the FSS alone (not that I'm saying you were suggesting that). There are other factors likely come into play as well. The new POIs came as a disappointment to some/many(?) while the giant postpone to end of 2020 certainly has repelled some of the more impatient players. Not sure how that synchronizes with the introduction of the FSS though. Too lazy to check right now.
To be fair, not a lot of players stopped right at the introduction of the FSS: it seems almost everyone decided to give it a fair try once it went live. Then there was DW2 as well. Increases tend to synchronize up with certain events nicely, decreases noticeably less so.
That's one interpretation of that data. The thing is that under the ADS system, you could see if a system to see if it's "worth exploring" once every 45 seconds to one minute. One of the chief complaints about the FSS is that completing this step this takes considerably longer. If new systems are being added at the same rate, and each system visited takes considerably longer to see if its "worth exploring," wouldn't that indicate that more people are actually exploring?
A good point, but not quite. The data also shows that the interest in scanning stuff, which is much easier now, has dropped from the FSS launch peak of 8.33 and the DW2 peak of 10 bodies per system on average to 4 these days. Bearing in mind that systems contain 10-12 bodies on average (depends on which part of the galaxy they are in), that at least means that people are cherry-picking more heavily now.
However, there is also another interesting statistic: the number of ELWs uploaded. This is actually quite comparable to the old system, because even the heaviest cherry-pickers wouldn't pass up on those (pre-FSS), unless they didn't actually notice them. Historically, after the Return and before the FSS, the ELW / Sys ratio moved around 0.5-0.6%. The introduction of the FSS increased that to a 0.74% peak (no surprise, as you get them handed to you on a silver platter now), but from the end of March to the end of May, it dropped down to 0.31%. The same level as much earlier days. In that sense, if you define "actual" exploration as bodies scanned, then with DW2 being over, activity was halved.
And while I'm sure that some "top 100" explorers can't or won't adapt to the FSS have quit exploring
You'll find that the majority of them didn't quit right at its launch. Looking at those heat maps, I'd say that most people gave it a fair go.
[...] it very well could be that the "slowdown" is due to systems taking longer to process, combined with more things to actually explore in the system.
Nope, the only things were added were a few more things to find, but there aren't any new environments to explore. This is just an anecdote, but personally, I don't know anyone who packed up at the launch of Chapter Four and quit without giving the FSS a good go.
I think you're over emphasizing the "systems per hour" statistic, and not looking at whole picture: there's now much more to do in a system while exploring.
A good point, but I've included other statistics now... and they paint a less pretty picture.
There is much more to do, sure, but only for the same amount of things to discover - that's not really a recipe for longevity. Personally, I don't count that as a good thing, and I'd rather have more to do and more to discover.
Mind you, this is assuming that you do full system scans, but most people don't. The majority gave that a fair try though, and obviously they've concluded it's not fun enough for them to continue doing so.
For picking cherries, which is the main activity (planned by the devs too), there's roughly the same amount of things to do, just in less time - and with less of the rarest rewards. Many more credits and tags though, plus surface POIs to discover - although Frontier have managed to shoot that in the foot, what with the long wait times for the frame rate-dependent scans to finish.
To be fair, there are two things that the Chapter Four update did well for me. Bear in mind that I like to analyse the crowd-sourced data. First, the star auto-scanner was great there. No more "why the bleep did you not scan even the arrival star when you scanned an Earth-like" moments. (This did happen often.) Second, even with the current rate of 4 bodies per system scanned, that's still a bit over twice as many as peak(!) levels before. Third, now that ammonia worlds are trivial to recognise (plus no travel times), people scan many more of them. So while exploration became less enjoyable for me, I do enjoy there being more data to go through.