How many is it, out of interest?
To illustrate -when I was in Utopia leadership (a few years back now), the power ran on about 20 people- that is, when each week something needed to be done, the spreadsheet matched almost exactly what was done in the UI. Others: when Utopia was undermined top to bottom it was two players (one Kumo, one Fed). Ben Ryder and myself flipped 95% of all Utopian systems BGS wise. Its why Powers hate PMFs appearing, because they have to spin several plates.
Admittedly the larger powers have many, many more players, but you are talking low thousands (as in < 2000) for total engagement. Things also get woolly with ZYADA since the player pool is shared and smaller Imp powers get 'guided'.
If you want to look yourself you can observe prep races and / by 750 (i.e. max cargo size), do the same for each system fort wise (and pay attention to the 'junk' systems close to a capital) and observe merit bombs.
The thing (for V1) you have to realize is that (unlike the BGS) merits are uncapped- a few people can do insane amounts. If all 13 million players were piling in PP V1 would most likely work better (ironically) since it was always designed to be a 'majority good'- 5C has an outsized effect because the pool of 'good' choices is smaller than what I assume Michael Brookes intended when FD did the maths.
Bear in mind this is just the PP side of things- in recent times Powers have shifted to the BGS, so you may find (ironically) many more PP BGS players than actuall 'pure' PP guys (moreso given the lack of room to expand).
In a self-selecting vote that was not publicised to the whole player-base.
How many multi-boxes is an unknown (or even how many players play more than one CMDR, one at a time).
How many play PP - already seems to have an answer from the quoted post.
Only Frontier know what the mode split is.
Its still a data point though, rough as it is.
You can count the responses yourself on the flash topics posted here- (admittedly its old now, and for a different design).
