Granted it wasn't an americas cup race, but the schooner "America" didn't belong in amongst the British fleet either. It was in a class of its own in its day.
The Americas cup boat of choice has always been a changing beast. Putting aside a few botch ups where they've put two completely different craft up against each other (and one has left the other for dead) the platform has nearly always been two boats similarly matched, but with room to innovate.
I dont think it's a case of the public being scared of sailing at all. I think it's far more a case of sailing being too hard to understand, and being generally boring to watch, I'm a mono sailor, but monohulls currently don't provide the excitement these boats do in the Americas cup.
I'd really like to know where this sentimental notion that the Americas cup should always be raced in monohulls is coming from? As much as it's what's happened in the past, it's never been a race held back by sentimental ideas.

To to me the Americas cup has always seemed to be the pinnacle of yacht racing. people throwing money into boats to see if they can go faster than their opponent. It is the F1 race of the yachting world.