not actually degoogled

Aside from vendor firmware, LineageOS is mostly deblobbed by default afaik. The remaining bits that connect to google (by default) like AGPS or captive portal are significantly less information than full google play services.

try to do it in ways that provide no privacy benefit

Replacing google play services with microg might have the same security downsides as regular google play services (privileged access), however, MicroG is open source. It still connects to Google, but sends significantly less data, and you can see exactly what it sends.

Break any semblance of security model

Rooting is one example, but access to it is often left up to the user. Keeping the bootloader unlocked has some major security downsides, but they're entirely for when an attacker has physical access. The privacy downsides of an unlocked bootloader do exist, but they're hard to exploit even with physical access.

ingnoring all of AOSP is Google

Yes, this is something you are forced to ignore with any custom Android ROM. Graphene, Divest, Calyx, etc all suffer from the same issue. Sending data to Google and privacy is not the same as being independant from Google developed software.

purely focussing on Google

On an AOSP or LineageOS based rom without preinstalled bloat, this is almost entirely up to user choice. You can choose to only install FOSS apps without trackers, or use Aurora store and install proprietary apps. You can choose to block network access for apps with trackers, or isolate them to a work profile and kill them in the background. It isn't good to focus only on Google, but it's a good starting point to use a rom without standard google play services.

While I agree that a hardened and privacy focused rom is better for privacy than regular LineageOS, privacy is not black and white. MicroG sending significantly less data is better than full access google play services sending all data. Not sending data is better than MicroG. That doesn't mean every user is able to use an entirely degoogled rom. Each person should decide for themselves what they're okay with and what they absolutely require on their own device. When someone is trying to get some privacy back, MicroG is a great option "in the middle" where as little functionality as possible is lost while sending as little data as possible. Discouraging that someone takes steps to improve their privacy just because it isn't perfect is not good, as that often results in someone not taking any steps towards privacy.

On the compatibility, while MicroG has some issues with specific apps, it does generally work (from what I hear from others). Not having google play services (or MicroG) can work, but it requires missing out on some google services like notifications for proprietary apps. For me personally, that's not a big issue, as I only use FOSS apps.

Greatest case for Graphene. Yes I find the need for a Pixel hilarious but it works soooo