HoB is a rune a lot of newer Darius players get, mainly for the same reason some get lethal tempo. The idea of getting 5 stacks sounds amazing. However, while this is quite useful(to an extent) in lane, it's near useless late game, as the utility the other runes give you are far more useful in the later game.
Titanic rushing first item is quite useless honestly. Well, not useless, but there are better items. Darius lacks mobility, and needs to stick on the opponent. Because of this, even though he has a quite a bit of slows, phage is a staple on Darius. The auto reset on titanic is nice, but thats all titanic provides. Darius has decent waveclear already, and his damage is already insanely high. What Darius needs is stickiness and tankiness. In a riven matchup, Riven has far much higher damage output, and since darius's sustain comes from his outer Q, riven can easily dash in and destroy darius in a short 1v1 burst trade. Building damage as darius destroys him. Building tank allows you to survive, and get the option to either try to punish her retreat, or retreat yourself. While HoB and Titanic grants an easier 5 stacks, by the time I get 5 stacks, I would die in a raw 1v1. In the scenario I would be incorrect and actually win this trade with this build/rune, riven can simply choose not to fight... making this a lose lose. The optimal way to build dari would be a phage item, with survivability tank stats (with sterraks most likely to negate enemy burst). Trick riven into making foolish 1v1s, and cheese her. If you succeed, you win lane. If you fail, then you get hard stomped....and seeing how a skilled riven can choose her fights (with darius's ideal playstyle is counterengage), Dari in no circumstance is an ideal fighter vs riven.