It's supposed to be a depiction of three things: Tokugawa's growing anxiety of the 'big' threat of Toyotomi, the fact that Hideyori would make a great shogun and leader of Japan plus the fact that he's just physically impressive and a gentle giant which means everyone would accept him and that would threaten Tokugawa's influence. He's a great guy who was meant to be Shogun but as history depicts, he was usurped by the older and more cunning Ieyasu.