A backup is not all a replacement for iCloud.

The point is to sync application data between native apps running on different (and even different kinds of) devices. PIM-style data (calendar, contacts, notes, bookmarks, and so forth) probably comes first for most people. Apple has also added useful stuff like Wi-Fi passwords and E-mail account configurations.

And then developers can create their own entries in the iCloud data store for their own apps. This is hugely useful.

I'm not aware of any similar facility that comes with Android, but I'd be happy to hear about it if there is.

You can use nextcloud for all pf that, not that I’d recommend it. There are solutions, even hosted ones.

Is there something else you'd recommend?

Regardless, though, if it's not built into the OS, developers can't rely on it being present on a majority of users' phones.