dnf has support for using the CoW support of Btrfs to make all the disk I/O more efficient. Might be why you're seeing dnf being more efficient, because my somewhat outdated experience is totally opposite.

YUM/DNF (and RPM itself) are very different beasts from what they used to be some time in the past. For some reason, updating repository metadata is still slow compared to APT, but installing packages is speedy enough. However, in terms of features it's just... better.

Two things that I especially appreciate: I can install things without knowing the package names, eg. "dnf install /usr/bin/foot 'perl(XML::Tiny)' 'pkgconfig(bwayland-client)' libaudit.so.1" will just work. These are especially useful when packaging stuff yourself because you can use these indirect references in your dependency list so it doesn't matter which package actually provides them.

I can also "sync" my system to a set of repositories with distro-sync, downgrading and/or replacing packages as necessary. I've had a few times with Ubuntu that I wished APT had this.

I also like that it does not have debconf. I don't have much love for debconf.

As I understand it the CoW support is for (optionally) taking filesystem snapshots before/after applying package upgrades, I don't think it inherently makes disk I/O more efficient. There are some other neat tricks that dnf does though. For example, in my experience dnf/rpm are smarter in the case where N packages need to run the same post-install step and run it once instead of apt/dpkg which might run it N times (examples: updating the man database, updating icon caches, updating ldconfig cache). And as the article points out, rpm packages are smarter about skipping post-install steps altogether for package updates.

In general it's my impression that dnf/rpm have been much more actively developed in the past few years than apt/dpkg. Depending on how long it's been since you last used it, they've made changes to the manifest format, the internal rpm database format, and rewritten a lot of parts of dnf in C for speed, and all of these have made a huge impact on the speed and usability of dnf.

If your outdated experience is with YUM as opposed to DNF, that could be why. DNF is much faster than YUM. However if you have used DNF then idk.

Using deltas for updates is a huge win for Fedora. On distros without delta updates, it's always a real pain in the ass when Wesnoth updates and you have to download half a gig of assets that are probably only a few kilobytes different from the last version.