Merrill Lynch’s federally chartered thrift was the most profitable institution among banks and thrifts that had a strong mortgage focus in their business. Merrill Lynch Trust Co. reported a whopping 15.02 percent return on assets through the first nine months of 2004, according to call report data. That made it the most profitable institution with over $50 million in assets and at least half of them tied up in mortgages or mortgage securities. …