Not as easy as people make him out to be. I'll address a few points:
Sure, he has unlimited ammunition, doesn't make him a better shooter. Q is still dodge-able, Kat/Akali/Karthus/Cass/Oriana has the same low-cost poke, with better accuracy.
His Q has good range, but still not be able to one shot ranged minions, i.e. he still has to AA. Alternatively he can also W-E to finish the wave, but then would have no escape for the next 20s, the lane would also be pushed which leaves him vulnerable to gank.
If he W-E to poke, which can only happen every 20s, he would have no wave clear or escape.
Diving "unscathed" is definitely an overstatement, R lets him lose aggro, but as soon as he hits you with whatever (Q/E/Ignite/AA) tower switches right back. The word you're looking for is "poke under tower", not "dive". And there are people who are better than him in this respect (Annie/Xerath/Cass/Karthus/Brand)
AD itemize is better, yes, but that'd be true for every AD mid (Riven/pant/Yas).
TLDR: Zed knows his trade, but not better than other champs in their respected roles, there are people with better poke, people with better burst, people with better aoe, with CC, or with tankiness. He just happens to be a stat ball, so are Irelia, Fiora or Yi.