alt Hacker NewsGrapheneOS (the project) might recommend for or against certain things in relation to their specific objectives, but that doesn't mean all GrapheneOS users have the same objectives or need to comply with the opinions of GrapheneOS.
For instance, I use GrapheneOS because it provides better security and privacy out of the box than LineageOS, but I'm also not so paranoid that I'm going to just blindly listen to advice against using F-Droid. What I want out of my Android instance is good security defaults with no bloatware, not to stop the NSA from looking at my travel photos and what HN articles I once looked at. It's okay if my OS is great but not perfect.
So yes, I am a GrapheneOS user who is [modestly] hurt by this. Signing in with a dummy account is just another one of those things that will end up being futile in years to come when Google requires iris scans, DNA samples, and anal probes in order to get a new account. Personally, I'd prefer installing whatever software I want on whatever devices I [pretend like] I own, without telemetry or jumping through hoops.
I've honestly never understood why F-Droid even still exists. Every time I've tried to use it (as recently as half a year ago) it's still a shitshow and never displays or updates apps correctly. Half the time an app showed up on the website that didn't show up on the phone app. The other half of the time even when I did get something installed, it would just never understand that an update existed and needed to download and update a given app. It's one of the worst pieces of software I've used in a while, and I can tolerate a good bit of jank from FOSS apps.