Have you tried https://apps.nextcloud.com/apps/memories - it solves all of my issues with photo management in nextcloud. (Together with the recognise app) I don't see why they haven't replaced the default photos app with this already...
I think improving the photos experience would have the biggest impact on home users, but nextcloud certainly seems to be chasing the enterprise/gov market in the EU? I'm not complaining!
But it is still worse compared to google photos/icloud photos/etc.
The issues I described above also happened with memories.
I think improving performance and memory usage in their webdav implementation would, by far, have the biggest impact.
Nextcloud is a fork of Owncloud, and Owncloud did the right thing to move away from php for the webdav implementation, though they are now rewriting it once again, which I don't really like, as they store the files and all information in some binary format.