Single servos are acceptable on an aircraft where control feedback forces are low enough for the pilot to fly in full manual control. This is definitely not the case for larger helicopters. I wouldn't want to fly any aircraft knowing that if the single hydraulics system failed I would be another passenger - I've had too many hydraulic failures in the past; some of them the result of a simple crush washer leak or flexible hose failure.
Also, without servos there can be no SAS or autopilot. Having been required to operate totally unstabilised, untrimmable/"floppy stick" helicopters IFR/IMC in the past (and properly trained to do it) I have no pressing desire to have to do so ever again.