--- Description ---
Now that font, icon theme, cursor and layout settings of GTK apps follow
Plasma/KDE/Qt preferences, the only options left in the GTK Application Style
page are the GTK2 and GTK3 themes. I suggest moving these to Application Style
page to reduce confusion. The 2 dropdowns could be displayed at the bottom of
the Application Style page (after the scrollable Qt style selection grid), or
on a second tab.
I propose behavioral changes as well: selecting a theme from either list that
has both GTK3 and GTK2 variants select the same theme in both dropdowns, for
the sake of consistency.
This way (I believe) customizing KDE would be a bit easier.
I didn't include steps to reproduce and system info as it would be irrelevant
in a design-related issue/feature request.