GWKdog I think you are reading Dominations.pl wrong. Not sure when it drops inactive players, but it shows many with last updates back in June. Updates only happen for players in an alliance over a certain glory (13-14k?). A player never joining an alliance won't show at all, those who leave and don't rejoin will show based on the last time they were in one. That last update time is a decent proxy for activity though - I would guess the vast majority of active players will be in an active alliance, if only for troop donations.
I searched for GPA accounts under the age setting on the site, which I assume is how you got your numbers of each age, as they are close to matching. Then I sorted by update time (last time they were seen in an alliance by the system) as a proxy for activity levels. There are 2159 pages covering 539k players in GPA, 250 players per page. By page 250, every player hadn't been updated in 6 days. By 350 that is 3 months, by 500 5 months. So conservatively, even assuming all the players on the first 250 pages are still playing, that is 62.5k GPA players. About 10% of the total in the database. 90% of GPA players in the database have quit.
For medieval, page 250 has accounts that are 2 months inactive. So fewer of those than GPA, not more. Classical about the same. Iron age is so short it isn't worth looking at. Enlightenment at page 250 also has accounts almost 2 months inactive. Everyone of those ages has well under 60k active players, as does global.
Page 250 of the industrial search still has players with their last login today. So there appear to be a lot more active industrials than any lower age. Globals are a month inactive on page 250. For atomics, p250 had players with logins yesterday. So more active atomics than active GPA as well, close to the industrial numbers. CWA doesn't even have that many players, but a higher percentage are active. The first 80 of 89 pages are players in an alliance updated today or yesterday, so 20k active.
That tracks with my experience, which is that most new players join an alliance, have fun for a bit, and then realize that this game is impossibly long and quit in Gunpowder or maybe enlightenment. More of those who have reached industrial stick around, they have adjusted to the reality of slow steady progress.
Based on those numbers, I would estimate the size of the active player base at under 500k. The majority of those are industrial or above, global and up is probably at least 30-40%. Nexon won't release official numbers, but those don't look sustainable to me, especially in the context of releasing new content for the next age that less than 20k players would be eligible for if released today. And anything that hurts industrial ages and up is hurting most of their active players.
Based on personal experience with IA alts, this rebalance hit IA hard. Much harder than my main CWA account, which already had maxed HTs and planes. I have dropped all of my alts now, they sit in that abandoned group. My main I play with free retrains a few battles a day. And I have stopped warring, as have half of our team's CWA accounts. Make of that what you will, but the rebalance wasn't surgical at all, it hit almost every active player hard.