It's suprizingly poor for many things. We don't actually care about any single material property, we care about ratios. For structural component you want high

It's suprizingly poor for many things. We don't actually care about any single material property, we care about ratios. For structural component you want high tensile strenght, high stiffness, high toughness, low weight and low price. If you compare natural diamond to Eglin steel, diamond only wins in weight. Carbon fiber is better in every way, the only problem remaining how you glue the fibers together. One area of interest has been diamond like carbon for coatings of mechanical parts. (It's actually pitch black, don't get too exited. And it actually doesn't share the precise crystal structure either.) Again it has few very disfavorable characteristics. Typically good wear resistance comes from good H/E ratio. ( Hardness= hardness, E= Youngs modulus = stiffness ) Now diamond is too stiff. Glass and rubber have better ratios, and both are increasingly used as coatings while DLC seems to be stuck in a very small niche. Threatened by shitloads of different carbides and nitrides which often have better H/E, better strenght and better toughness, while being only slightly less hard. (Strenght and hardness are different things.) Also DLC dissolves into steel and burns in very hot temperatures. These are shared by actual diamonds. So diamond doesn't even cut it in hardcore cutting blades, where extreme hardness and compressive strenght would otherwise be useful. Only concrete and aluminum are routinely cut with diamond.