To everyone stating to use Google apps for things such as Calendar, this is not a solid option. You cannot (to my knowledge) connect to WebDAV to sync. And even if you could, it would not work if you denied network permissions, which means you are using the app online which from a privacy concerned perspective, is not a nice peace of mind.
Also I disagree about first party apps stomping independent apps. In terms of amount of people using it? Yeah of course, most mainstream users don't even know what sideloading apps are. They use what come on their device. However feature wise? There are many libre software that is used in professional and personal fields that stomp first party software in many aspects. Unfortunately in general, yes I agree that UI design is not a huge skill many libre developers seem to have haha. However, Google does have standards, and it would not be a bad idea imo for a developer to simply take say Google Calendar, and clone the design aspect of it, remove a few privacy unfriendly things, and integrate stuff such as webdav capability. Basically a clone of the app, however libre. Yes I get this takes work, however would it not be in Graphene's interest to attempt a crowdfunding to fund such a thing and actually find developers who are willing to take a small pay to encourage them to create an appset that rivals Google apps?
Also I believe FSF does have a support funding program too you can try to qualify for, maybe something like this would be of interest?
These are just ideas. However, these would be beneficial not just to Graphene, but the libre Android community as a whole.
And again you will always have the split of people who just want bare minimum apps.. in that case all they have to do is not install them/disable them and use the pre-existing hundreds of minimal apps that are already out there. But for people who WANT feature sets rivaling first party applications.. well there really isn't much out there at all.