If you missed the limited time sourdough melts at Arby's .... don't you worry, you didn't miss much. It's a sad thing when good fast food goes grossly mediocre. While the Arby's Beef N'Cheddar is sometimes a thing of beauty (o, that onion roll! that melted cheese!), the Roast Beef Soughdough Melt, which is just the same thing except with sourdough bread, barely even deserves to wipe the cheesy drips off your chin.
Perhaps I'm being too harsh. After all, the beef was fine and the cheese was fine, it's really a failing of the bread. The problem is that it's not sourdough. I'm pretty sure it's just white bread spritzed with vinegar. And it's not even toasted fake sourdough bread. Don't let the brown top fool you, because just underneath it's spongy and soft like the purest of Wonder bread. Which leads me to suspect that the guy in the back holding the mister of vinegar also has a paintbrush of brown food coloring at his disposal.