Dean and Cas do share a more profound bond even without any "subtext." In the Winchester history books/gospel/legend, they are Adams and Jefferson, Brutus and Caesar, Achilles and Patroclus. There are no accurate parallels in history or legend for the bond of the two Winchester brothers. But Sam and Cas have their own connection as members of Team Free Will 1.0 and 2.0. They are two of the unfortunate members of the I-Thought-I-Was-Saving-or-Improving-the-World-But-I-Was-Tricked-into-Triggering-Its-Near-Destruction Club. Other members include Pandora, Adam, and Eve. They formed their own I-Died-Trying-to-Make-it-Right-But-I-Was-Brought-Back-subchapter. They, along with Mary, Dean, and Eileen, formed the I-Died-But-I Got-Better Club. They both could write an article, "How to Deal when Lucifer in Your Head Won't Stop Singing Stairway to Heaven." It wouldn't be much help to anyone. The solutions of having your angel friend shift it or wake up when the prophet finds the angel tablet, get trapped in purgatory, and then get brought back again didn't really apply to anyone else.
They are two of Jack's three fathers and two of the three founding and permanent members of the Let's-Not-Kill- Jack- Club. In general, they are both members of Team Ask Questions Then Shoot. They also both frequently walk in with a meticulously researched and thought-out plan. Which they then have to throw out the window when they find themselves in an unexpected jam.
Dean, much to their frustration would go in with no plan and guns blazing. But he would still see the unexpected complication coming before it happened and come up with a brilliant strategic plan in the few minutes or even seconds, he had. Lucky bastard. Sam and Cas's biggest link will always be the number of times they think, "Damn it, Dean!", "Really, Dean?" or just "Dean!" in a tone of complete exasperation simultaneously.