Talking about snobby and rude developers and in the same moment asking in the Nextcloud forum how the gallery of other projects is? Well, this is brash.
Why don’t you contribute to the project by proposing an Pull Request? If you are no developer, then why don’t you open issues with concrete topics that bother you instead of this blurry “all not good” which does neither help the developers nor other users, because it could mean everything and nothing?
The project you mentioned focuses a lot on the file synchronization mechanism. You will find the bigger ecosystem for 3rd party apps at Nextcloud. There are ideas to reenable the old gallery app. Of course you are welcome to fork and maintain this app.
Disclaimer: I am not related to Nextcloud GmbH in any way.