Let me try to paraphrase the sentence for you.
'Most managers are not capable of creating successful corporations when they have as few resources as Alfred Sloan had at GM when he took control.'
At the time Sloan became chairman, GM had less than one-fifth of the U.S. auto market share while Ford had more than half. By 1931, GM achieved the almost unimaginable by surpassing Ford once and for all. Through Sloan's three decades of innovation, leadership and guidance, GM became the world's largest industrial corporation.
In essence, Sloan utilized three decades of innovation, leadership and guidance to 'stitch an industrial triumph' within a company that was a 'vast bankrupt junkyard'... a company that had less than a one-fifth share of the US auto market.
Does this help?