Natch. Losing two islands and the fallout from that alone would have killed millions, every Endbringer attack has the potential to wipe out entire cities since anyone in a Simurgh containment zone is effectively dead, we can probably just ignore the Swiss entirely for the same reason and who knows whats going on in Africa, where society has completely broken down, or China, who are...well, China cranked up to about a million. And thats ignoring folks like the Nine, the Three Blasphemes, Ash Beast, Nilbog, the Machine Army and whatever the fuck Sleeper is also screwing with and murdering entire towns and cities. I would be genuinely surprised if the population graph of Earth Bet isnt going downwards at a worryingly sharp angle.
While matching IRL Earth in absolute population
is absurd, it doesn't seem necessary for Earth Bet's population to be precipitously declining.
The Endbringers don't prioritize casualties. It's entirely possible that their sandbagging allows sufficient numbers of civilians to escape or take shelter after the Endbringer Truce and similar protocols came into being, significantly reducing non-parahuman death toll.
Similarly, Nilbog was a relatively sudden threat, but there
was some level of warning, and if PRT field comm channels are good enough then evacuation efforts might have begun early with the PRT (+ Protectorate?) delaying Nilbog's forces in the meanwhile, particularly if he didn't fully commit his "subjects" at first.
If I recall correctly, Sleeper didn't do much by the beginning of Worm, though I could be wrong.
I don't think Ash Beast actively seeks out victims, so it would be theoretically possible for local traditions to develop allowing people to detect his approach and run away.
And considering my general impression of it in-story, I wouldn't be surprised if the CUI had mandatory breeding practices to get more capes to conscript, which (considering cape-augmented forces are much more effective enforcers than humans alone) could be successful enough to offset their fatalities.
A higher birth rate also seems viable through a combination of multiple factors unmentioned in story, like lower education rates (which some studies correlate with higher population fertility rates) and governmental discouragement of contraception compared to IRL Earth driving up prices and inconveniences.
With the Fedora'd Hand dealing with most
new threats before they grow particularly large, there are at least plausible worlds where Earth Bet has a lower but stable population rate.