You seem to be aware that correlation = causation.
The thing is as DRM has been reduced the market as grown. Perhaps there's a correlation, perhaps not.But having been involved with PC gamers for decades my anecdotal belief is there is a correlation.
The market has grown because gaming on PC has become a better experience all around, with services like Steam streamlining the process and helping to make PC the most cost effective way to play.
Only bad games get pirated?
They better spend those 100k € in games additional features.
Wanna fight piracy? Make sure your game is good, simple as that.
Having a good game might financially insulate you a bit from the effects of piracy. But it's not an anti-theft.