It was a DC book that kicked off the Silver Age of comics with Showcase #4 in 1956. Fantastic Four #1 didn't debut until 1961 and it took more than a decade before Marvel comics sales overtook DC. Stan had given up writing full time by then. For the vast majority of his career at Marvel he essentially functioned as a brand ambassador and pitch man. US comics got stuck in a weird superhero monoculture for a couple of decades. Meanwhile over in France, Japan and Korea there was a full scale mass market comic book revolution that eclipses the US industry in scale by an order of magnitude. Stan was important for sure , but his greatest production was himself.