There are lots of reasons to like passkeys from a technical/enterprise standpoint, but I do think you're missing the critical issue the article is speaking to: digital sovereignty.
Passkeys, while more secure in the average usecase, shift the balance of control over your access to services. Yes, you can no longer write your password down on a post-it and leak it in a photo—thats's a good property. But trading that at the expense of your freedom to run software as you see fit on hardware you bought and paid for? For many people, myself included, that's not an acceptable tradeoff. There are plenty of tools and systems around passwords that folks can use to make passwords+2FA match or even exceed the security properties of passkeys.
The thing that should chill everyone is the fact that built into the standard is a switch (given to service providers, not users) that locks out the people that do want to have control of their digital infrastructure. Not everyone can or should be expected to run like that, but they should not be blocked from doing so. Similar with the Right to Repair; not everyone can exercise that right on their own, but no one should be prevented from repairing what they bought.
Similary, I do believe it's my neighbor's right to practice a religion of their choosing. So if the government tries to prevent them from doing that, I'm going to go grab my pitchfork, not because I share their religion, but because they should be able to make that choice. Likewise, while I might not want to exert control over how my credentials are backed up, I still reserve the right to do it, and support anyone else's ability to do it.
And to address the slippery slope objection, I have to point out that this is not particularly theoretical. When Big Tech has provided service providers with the opportunity to enforce restrictions on your device, service providers have used it. Widevine DRM, Google Play Protect, etc.. It's why my LineageOS phone can't use banking apps, which is a shame since some features like Zelle payments are specifically a mobile-only feature, and so I cannot use it anymore. I either run my phone to the exact specs and settings that my bank and Google prefer, or I'm denied access to basic banking anywhere but my desktop (and who knows how long until the block my access there, I run Linux afterall).
I do not trust Big Tech with my devices, and passkeys increase their capability to deny anyone who doesn't buy into their ecosystem, and further entrenches those who already are. I for one find that despicable, and an unacceptable tradeoff. There's no reason it has to be this way though, passkeys could have been the best of both worlds. However, they've been compromised with features that serve platforms at the expense of user freedom. It's the kind of disempowerment that happens when you give the reins to power-hungry, profit-seeking corporations.