As hundreds of TD Securities managing directors gathered at the Encore hotel overlooking Boston Harbor in June, there was a celebratory atmosphere in the air. Less publicly, there was grousing as well. The buoyant mood at the multiday meeting was partly because Toronto-Dominion Bank’s takeover of New York investment bank Cowen Inc. — completed in 2023 — had cleared its last legal hurdle just months earlier, allowing the firms’ traders to finally work together in person. The event also marked the first ti ...