doesn't the Queen ride around in a S76?
The quick answer is 'Yes' but ....
... as with all questions in the field of aeronautics its often not as clear cut as that.
The Royal Household bought the S-76 for its own presumably considered reasons as the type most likely to fit in with looking the part [replacing a Sikorsky derived Wessex] and performing the mission.
But I understand there are occasions [and missions] where the 76 is set aside and an A109 Power is used. I believe that this is a performance issue out of certain locations.
Equally I suspect that if the Queen had bought a A109 there would be missions where a S76 or similar would be brought in.
Does the use of a Sikorsky by the Queen 'prove' that the AgustaWestland EH101 is a faulty design? Or does the occasional substitution of an [AgustaWestland] A109 prove that the S76 is not up to the job?
No, on all counts.