I woudn't call it a disaster, but a disappointment that leads to the same result. Every time I think about upgrading to KDE5 (LM17.3/KDE4), I open a VM with a KDE5 desktop (from another distro) and I change my mind. I took the ride from 3 to 4. Just when it started getting stable, they went to 5. Is it worth investing time again? How many more years of instability. They had 5 different Desktop Views in kde4, 2 in kde5. I spent a lot of time trying to get Grouping Desktop and Groups to work. A number of features introduced in 4, don't exist in 5, so knowledge was nontransferable and time wasted. And now with a
qt6 in the works. Are we in for a repeat? Qt6 and Wayland are going to make for some interesting times. It might be a great experimental desktop, but imho not a practical stable office desktop for use today. Just simple things that I have done for years can cause a crash. They have changed locations of config files multiple times. I just tried a script that uses kdialog, --caption is no longer supported. No problem, use --title. But the progress bar property wasCancelled doesn't work and the example at techbase works differently in kde5 than kde4. Someone worked really hard on the kde4 doc at techbase.kde.org, userbase.kde.org, community.kde.org. It got me through the kde4 learning curve, but it hasn't been updated to reflect kde5. The environment of support isn't as much fun and tempers are short.
I stopped using KDE's PIM in 4, but that also meant getting rid of little things like kalarm. I like konsole, dolphin, okular, k3b, kate. I have some code invested in kate. Little things are annoying, like renaming ksnapshot, Spectacle. Although I read something about replacing that with KScreenGenie. And I'm not a fan of the flat icons and a number of the new UI's. It just doesn't seem as intuitive and natural.
In some ways, I feel this is a decision between qt and gtk. I read once that while lxde was upgrading to gnome3 they decided to change to qt, thus
lxqt. But it seems they both exist. lxde is gtk based and lxqt is qt based. kde is qt based, while cinnamon, mate, xfce gnome are gtk based. There seems to be a greater relationship disconnect between qt and kde, than there is between gtk and gnome/cinnamon/mate, so kde devs are more susceptible to what/when qt does things which amplifies the problems. If you work with vendors and other software, you begin to notice where they have problems and their preferences.