At this point I feel like I'm posting off-topic while attempting to post on-topic.
I'm in Mobius PVE about 80% of my time, solo about 18% and open for about 2%.
Based on my limited time in open, I do think there are more people in open.
However, I see many, many people in Mobius PVE. I ran into a random CMDR in the Spirograph nebula over 1000ly from the bubble. I ran into a random CMDR while exploring the "Dav's Hope" settlement. I've run into a few CMDRs in different random HazRES, away from CGs or "special" systems. I saw dozens of CMDRs at the different alien ruin sites when I visited them. I see many multiple CMDRs at every CG, most engineer bases, and most of the "special" systems(Aditi, Fehu, Quince, Sothis, 17 Draconis, Shu Babassi, etc). So, point is, regardless of the actual population, I don't have any problem being instanced with plenty of other CMDRs.
And just to echo one thing that was said earlier, most people in the PG have been very friendly. Easy to form wings, exchange an "o7" or whatever. I joined Mobius early in my game because I was "scared" of open. I've progressed well beyond that, but I still play in Mobius because I like the people and interactions better than open.