Well they tied it into DLC and so obviously quite a few didn't know it. But you get a mission for him, and then if you bring him on missions he brings his insight. But ever since the first Mass Effect, Protheans were this long gone race, one of the best in the galaxy, last act was to warn future generations, etc.
And then you have this guy, who basically retcons what most believed about them, and just changes what people's ideas were of who they are, what they did, why they died. Would have been better if they were always a mystery in a sense. Don't need to explain EVERYTHING in a sense you know.
For me, with halo, the forerunners were this long gone race, who were the ancestors to humans in a sense. They left behind these brilliant rings, structures and technology. The covenant used what they found to justify their expansion/genocide of humans etc. Don't really know who they were, what happened or what they did. Just that humans 'were forerunner, chief was a reclaimer. Then it became forerunners defeated humanity, and have space magic telekinesis, and somehow Librarian singlehandedly was responsible for humanity developing Spartans, their AI and it was never his luck or ability, but 'fate'.
I wouldn't have even used forerunners for a new trilogy. I'd have used another alien type race who knew of the forerunners, even fought with them and were banished from the Milky Way Galaxy and the destruction of the Ark, drew them back. But they never knew about the Flood etc.
