I am not a project member so I cannot speak for GrapheneOS, but maybe I can help clear up some misunderstandings.

>insistence on not supporting MicroG leads to poor UX,

The problem they are trying to solve is apps not working without the presence of Google Mobile Services or Google Play. They don't want to compromise by having a component with high privileges integrated in their image that involves security issues like signature spoofing.

MicroG will send less data to Google partly because it is simply an incomplete implementation of the features offered by GMS (sanboxed-google-play appp compatibility is quite a bit higher), partly because the access is more granular or there are choices offered for services like location (GrapheneOS provides non-Google location services and community support on only installing and enabling the parts you need for specific app features to work). UX is not adversely affected, but if you want to use a privileged app bypassing security checks and sending data to Google anyway then you have the freedom to compile microG with it integrated if you would like.

>They also seem to be very opinionated about (not) using a firewall for privacy, like NetGuard, instead recommending some weird alternatives like DNS firewalls

GrapheneOS tries to implement or end encourage sustainable approaches to privacy and security, and this partially means approaches that don't break if the adversary knows what you are doing.

Egress/outbound traffic filtering is fundamentally unworkable. Apps do not have to connect to known privacy a invasive third party domains to violate your privacy or expose your data to extra parties, they can simply send anything they want to their own servers and do anything they like with the data. From my understanding this is why GrapheneOS do not want to encourage the approach of blocking apps from connecting to certain domains/addresses.

Instead they tackle the problem at its source by providing a direct AND indirect network access toggle which cuts off an apps access to the outernet without letting the app know (pretends the network is down). This makes it non trivial for apps to exfiltrate data and as a side effect can provide benefits like data conservation (for capped plans).

>instead recommending some weird alternatives like DNS firewalls.

DNS based solutions are offered (not promoted) if you want more control over your DNS query resolvers or you want to improve your quality of experience by blocking advertisements and malvertising domains.

>they (heavily) prioritize security over privacy.

Can you point out another OS project with real privacy features like a network permission, sensors data access permission, contact access scopes, storage access scopes, per connection MAC randomisation and so on? https://eylenburg.github.io/android_comparison.htm They have even more plans for privacy like location scopes, anti-fingerprinting for Vanadium browser and maybe AnonymisedDNSCrypt/Oblivious DNS and probably more they haven't mentioned. If you suggest some more on their issue tracker they may get back to it when they have the resources.