Well letting other people choose for you is not really discovery. When too many people abdicate this responsibility, art becone whatever profitable mush advertisers shovel in our face.
Critics and mainsteam media has existed for as long as media has. They don't choose for you. They just help judge whenever a movie might be worth watching.
It's not like I watch a movie just beaucse it's mainstream. I watch some mainstream movies because they specifically are good.
And isn't really the most highly rated and well liked movies in existance mainstream by definition?