I've personally had the same install across six Ubuntu installs in total and I know other people like that as well. Anecdotal experience but so is claiming Ubuntu's breakage ratio is higher.
There are certain situations where a Debian upgrade will break a specific package - maybe due to upstream messing up really badly, or maybe due to some unusual way of configuring it. But in that case, the release notes that Debian publishes for each release would cover that particular problem for sure. Mistakes happen, and noone's perfect - but Debian tries to be, and they're very near that ideal in terms of ensuring your ability to upgrade your installation.
Personally, I don't think that Ubuntu is less perfect that Debian wrt. upgrade quality, it's just that (it seems to me that) the workforce is not as large, and that they also have other projects on their plate (not to say it should be that way or not, I'm merely trying to state the facts).
So if libreoffice depends on package P, and that one is not ready, is Debian going to simply drop libreoffice until next release?
At a very high level, it works like this:
New versions of stuff go into Unstable. When they've been tested a while they get pushed to Testing. Periodically Testing is frozen and branched into a new Stable release. If a package doesn't make it into Testing before the freeze then it's out of luck and has to wait for the next release.
For example, assume libreoffice 1.0 and libfoo 1.0 are in Unstable, Testing and Stable. If libreoffice 1.1 comes out and depends on libfoo 1.1, but libfoo 1.1 is broken in Unstable, then libfoo 1.1 and libreoffice 1.1 won't be pushed to Testing until the issue is fixed. If they don't make it into Testing before the release freeze then the next stable will ship with libreoffice 1.0.
After the freeze, when the libfoo 1.1 is fixed in Unstable, then libreoffice 1.1 and libfoo 1.1 will go into Testing and wait for the next Stable to get branched.
"the Lubuntu team does not support upgrading from 18.04 or below to any greater release. Doing so will result in a broken system. If you are on 18.04 or below and would like to upgrade, please do a fresh install."
Note that 18.04 was also LTS, so whoever tries to upgrade from one LTS to another, will probably be able to start the process (like before) but at the end will with huge probability be better off just biting the bullet... and fresh install.
If the "people you know" upgrade faster then LTS to LTS they won't see a problem this time.
But being able to upgrade from one LTS to the next LTS is completely reasonable user expectation. I don't even want to try to prove that it will be broken this time.
The one I replied to said Ubuntu not Lubuntu. Big difference.
In order of stability from most to least.
LTS -> Bleeding Edge -> 6 month release cycle distros
Stuff like Ubuntu non LTS seems to break as much as bleeding edge but take longer to fix it. It's the worst of both worlds.