For that particular point (Relative Size, Ganking vs. All PvP) the months I checked for comparison were “all PvP listed on Zkillboard”. So as others pointed out, it won’t get every PvP encounter and it won’t classify everything perfectly.
For “quality of the data” discussions, keep in mind that we’re likely talking “order of magnitude” levels of accuracy here. There are ways to pull more accurate data but for a quick overview this is sufficient.
As for where do most encounters occur, I’m not sure I could narrow it down based on your criteria of quality vs. ISK value. However (again, quick survey), Zkill says:
June 2022 Zkillboard, Victims Only:
High Sec: 44,293 4.53T Isk
Low Sec: 81,683 7.69T
Null: 193,926 22.06T
WH: 41,708 7.08T
Abyss: 30,049 2.52T
So we can see Null sec basically accounts for half of all kills and value, then Low at 20%, High and WH space a bit over 10% each, and Abyss around 7%.
ISK value is subjective in terms of emotional impact/significance to the individuals but it is significant in terms of destruction vs. economy and grind-time to replace, etc.
This is a relatively key design issue of EVE and one of the reasons for this thread. The significant part being that lots of people (and apparently CCP) look at destruction and PvP as something we “should” be doing, simply because “EVE is a PvP game” or “it’s needed for the economy”.
So CCP does things like ESS in Null where they’re basically trying to nerf player incomes until they’re forced to PvP. Which is a really poor and lame way to go about it.
Gamers take the actions that move their goals forward and are likely to provide a positive outcome in some aspect of their value axis. Gamers will fight for glory, for position on a scoreboard, for profit, for honor (sometimes), for grudges, for relative advantage, etc.
If players aren’t PvPing in EVE as much as they “should”, then it means CCP has got the nuts and bolts, pros and cons, of PvPing wrong.