Bluesky knows full well it's not operating a real federated service
Better tell that to Blacksky, Eurosky, etc.
The vast majority of people stay on the primary PDS, relay, etc namely because Bluesky hasn't proven itself to be some evil overlord pursuing insidious goals. If that were to ever occur, people would just migrate. Unlike with ActivityPub (Mastodon), ATProto allows for true migration. Your content isn't tied and linked to a specific server - it's more like a URL on an arbitrary domain, and you can just change the "domain" (the PDS). Everything is timestamped and cryptographically signed, so if you download a backup of your content, you can just reupload it somewhere else and it continues to remain linked into the whole ecosystem.
More to the point, primary Bluesky servers have gone down and third parties like Blacksky remained operational, very much demonstrating that the network is federated.
Also, re: this from the header:
" and by the end of October last year, it had reportedly seen a 40% drop in daily mobile active users over the past 12 months."
... is cherry picking. If you graph users, you'll see that - like most sites - new users tend to arrive in big "spikes", triggered either by events at other social media platforms, or major news cycles (such as elections). Most new users to a site are not "sticky". Some drop off in days, some in weeks, some in months, etc, but this slowly levels out, and the rest are "sticky". With Bluesky, usually half or so of new users stick around, which is an unusually high percentage. If you measure from a new-arrivals spike, of course you see a "dropoff", but you see that for any site. The question is, how is the long-term trend of users that stick around? If you cancel out the spike pattern, Bluesky has a long-term population of around 600k daily posters / 1M daily likers / 300k daily followers.
What you can say is there haven't been any big new user spikes since late 2024 / early 2025. That said, there kinda was some serious news going on in late 2024 / early 2025....