I live in MA and have had many mayo based Lobster Rolls at fish shacks by the ocean many times. They are authentic too. You will also find some spots that don't use mayo but instead drawn butter. They are authentic too.
I did think the lobster roll at CCH had too much mayo. It was also more knuckle meat than chucks of lobster, I agree. I thought the one at Captsain's Grill was mayo based too. Am I wrong?
I was disappointed in the one at F & W this year.