Ref AEW.
The higher you go the further the radar horizon. As a minimum I'd want the AEW at FL250, ideally FL350+.
The speed of a helo severely limits it's use/flexibility. It can't be used to accompany a CAMAO and can't be rapidly moved to face a new threat axis. it's also very vulnerable as it can't retrograde out of range if targeted.
it's better than nothing, but nobody would use rotary if fixed wing was an option.