When running a kde application as root i see that for example is not using the style and fonts set in systemsettings (root), but instead is using the style and fonts configured in qtconfig.

Runing kde apps as a regular user is quite different and here it does in fact follows the definitions set in systemsettings.

Reproducible: Always

Steps to Reproduce:
Login as root as run a kde application, and will not use the definitions set in systemsettings (set as root).

To change for example the style of a kde app run as root, also as root run qtconfig and change the style.
Actual Results:  
Runing systemsettings as root and setting a style will not make any difference for the kde apps run as root.

Expected Results:  
The kde apps run as root should follow whats set in systemsettings as root.