For rotary, it is either VFR or a full IR. No IMC/IR(lite) ratings. This is primarily due to the unstable nature of light, SEP helicopters.
Please elaborate why an airplane is more stable than a helo, assuming identical IFR instrumentation.
Especially how a full IR rated PIC makes the helo more stable
Neither has to comply to the "full IFR" ATC raido guided heading, height and frequency changes. Both just monitor the famous six, with the helo having more time to react due to lower airspeed.