Melee range is not something Zed's kit is though. His auto attack is, but like Darius he has a kit built to win lane. The difference is that Darius will win if he can keep Zed in melee range the whole time, but when comparing the kits together, Zed has plenty of ways to escape and dodge significant chunks of damage.
This is talking about rushing a triforce anyways. Darius would have the upper hand on Zed if he built tankier as he can still sustain and output big numbers while significantly reducing Zed's. But beating Zed is never a matter of trying to out glass cannon him.
Vs champions like Talon or Diana, they are melee assassins that I could see Darius dominating. To do anything they need to go in hard. Zed does not need to, he can keep his distance.
Also you don't need be to be above gold to hit Q and point at a low health creep. Or shadow away. Or even ult while your Q is casting. It's simple mechanics. Just remember, at equal skill levels, the numbers do not support Darius in a glass cannon v Glass cannon build.
And I wasn't implying Zed's kit is overloaded, he just sports heavy damage with a bit of mobility. Zed rolling your face doesn't mean he's overloaded.