All the stuff in Dropbox can be accessed by my wife on her devices. If it was in iCloud she couldn’t see it. We have a lot of docs we both need full access to. Also use Dropbox to share some docs with wider family, not possible with iCloud.
I have iCloud storage because I have an iCloud photos library for my notebook and record type photos, plus Mail and iCloud backups. Also the iCloud storage is family shared with wife. Might be able to squeeze this down to the 50GB band and save half a cup of coffee per month.
Our joint main photos library is the Lightroom library (cloudy version) which is fully accessible to both of us on all devices.
Maybe one day Apple will get their sharing act together and match the capabilities of Dropbox and Lightroom for sharing docs and photos between people on different Apple IDs.