Before Sandro/Munir there were Isaac Cuenca and Cristian Tello. They failed, too. Messi to this day is the best to break through our ranks and play for Barcelona in terms of forwards, second would be Pedro, probably. La Masia is just not the factory for world class forwards as much as I dislike settling on this.
Whenever I watch videos like "THE NEW MESSI, 10 years old, SKILL & GOALS WOW!" I start thinking how many years it took for someone to shook the world after Maradona? 20 years. Barca got lucky having Lionel Messi develop at the right time along the wizard Ronaldinho was. The next phenomenal footballer will probably come out somewhere else, not in Barcelona. Chances for that kid to be Argentine are 90%.