As a quick thing about this, you have to compare items as a whole.
Duskblade, Youmuu's, etc. all have much more AD than, for example, LDR.
Especially early game, flat AD is a very important stat. So building items that give 60+ AD as well as 10-20 lethality is a really good stat profile for killing Ashe and the like.
Ravenous Hydra appears to still be exceptionally strong, arguably overpowered. It's almost certainly Zed's best first item. Not going to debate that one. That said, for second item Zed, both Duskblade and Prowler's appear to out-perform Cleaver. So players are opting toward bruisery target-agnostic builds, but lethality appears to out-perform.