Desktop Themes and Plasma 5

Running F22 BTC3 and it seems as if the only Desktop Themes which allows the Network widgets to display properly are either Breeze or Air. Is it safe to assume that is due to the Oxygen theme, for one, being designed for KDE4? I've not tried to install the old Workspaces on F22, but think that can be done, but I'm wonder if there is any way to prevent themes not known to work properly, or known to not work properly, in Plasma 5 being listed as available for use? Also, in System Settings, under Appearance there is a "Look and Feel" but only "Breeze" is available and no way to add more selections. Is this by design? -- If you can't laugh at yourself, others will gladly oblige.