It would be easier to script with kioclient5 if it behaved like gtk-launch, which allows to execute .desktop files simply by running their filename directly: gtk-launch org.kde.dolphin.desktop or gtk-launch org.kde.dolphin (both work) Currently the only syntax available for kioclient5 to open a .desktop file is kioclient5 exec /usr/share/applications/org.kde.dolphin.desktop
I think for that functionality you can use kstart: kstart5 --application org.kde.dolphin
Closing, feel free to reopen if you disagree :)