There's a lot going for this. Modern composite materials are much lighter than older ones for a given strength, for one thing. Not even engines need much metal in them, these days. Lighter structure needs less helium to give it bouyancy.

In actual fact, modern materials and tech could make it safe to use hydrogen again. Properly-sealed tanks and isolated electrics woiuld certainly reduce the fire hazard.

As to slow, as a culture we have become too obsessive about speed. I think it's so we don't have to plan ahead and think about travel and logistics as much as we used to.