KDE guy here.

Konsole is a fantastic and very mature terminal emulator, but it does have some real gaps that reveal its age.

The Qt toolkit that most KDE software is based on at some point introduced a next-gen toolkit-within-a-toolkit called Qt Quick, which most of our newer apps are written in. However, in its library form Konsole can only be embedded into apps that use the old gen toolkit. This is a real impediment to some efforts.

The old gen toolkit also typically doesn't use Vulkan or OpenGL for rendering (the new one supports both), and so Konsole's terminal renderer doesn't either. Konsole's real-world performance during use is arguably just fine, but it does leave a lot of performance and battery life on the table.

libghostty also has somewhat wider support for newer stuff like Kitty protocols, even though Konsole certainly trumps it in support for older stuff (like sixels).

There's some other shortcomings to Konsole that are not inherent to the technology, like accessibility support not quite being where it should be.

And while the default UI is, in most distros, OK, there sure is a lot of spiderwebs and spacebar heating lurking in the settings dialogs (of which there are strangely many). It's also a bit dated vs. our HIG at the moment.

Which is to say, these projects can and do have a point, especially if they provide a nice library instead of hoarding all the good to themselves.