Yeah, it's all conjecture and capturing snippets of info to try and piece together the bigger picture.
Like you said, only FD know the real numbers and they're not in the habit of sharing, so I suppose these kind of threads will continue to appear.
I do think the steam concurrent player count is fairly representative of the games popularity (for want of a better word) amongst the player base, though not definitive.
Steam charts certainly tells us something about the state of the game (if we ignore external factors like the weather etc.), we don't know if the active player base or playtime per player increases / decreases though. As an example (it's simplified but the rules still apply):
Let's say the average person plays 1 hour each day and playtime would be distributed evenly over the day, size of the active community on steam is 24000 (all assumptions are wrong, but that doesn't matter). In that case concurrent players would always be at 1000, correct?
Now let's say half the people leave the game, concurrent players would be at 500.
However, if nobody leaves the game but people play less, let's say 0.5 hours per day, concurrent players would also be at 500.
So we can't know if people quit or play less by looking at Steam charts. If we add external factors like the weather and end of lockdown it gets even more difficult to make assumptions about the player base. And that's just looking at average player numbers. If we also include peaks which usually happen around release because lots of players try it simultaneously it gets completely silly.
On the other hand Steamcharts certainly tells us about reception. If Odyssey would be the most awesome thing in the world, I am pretty sure that more people spend more time in it which would also be noticeable by looking at Steam charts. So by looking at it I guess Odyssey wasn't a success.
The last question is, did we really need Steam charts for that?
