The phoronix article misses what makes the project important:

Konsole is very intertwined with the older of the two user interface tech stacks in Qt, QWidget. QWidget typically renders using the CPU, and so does Konsole. Newer KDE software (including Plasma itself) typically uses Qt Quick and benefits from GPU acceleration via Vulkan or OpenGL instead. This is what Kwi does as well. For certain terminal applications the performance gain (3x-35x faster than Konsole depending on what's being benchmarked) can make an actual big difference in the user experience, but generally it should also help reduce battery usage.

I know at least one developper who chose to use libadwaita instead of Kirigami because QtQuick didn't have a good terminal widget.