>CalDAV, CardDAV, and SMB are baked into iOS, whereas these are onerous to set up on Android

I can only speak to SMB but it is not hard on Android. I use a longtime third party app so not sure what the state of native support is but it works just fine for me, including over VPN

Sounds like you're Apple now, but would love to hear what you're actually using for DAV on Android if at all?