He needs harass early game to be relevant at all in terms of laning power.
Also, Q does fuck all for damage unless you hit it with first hit
Zed's harass is NOTHING compared to Lulu's, Leblanc's zoning, Ahri's 10x safer harass, and Vlad turning his enemy into a health potion every 5 seconds. Zed neeeeeeeeeds harass to not get zoned harder than a mid lane taric before hes level 6.
Without harass, for Zed to claim enough hold on the lane to break a zone at any point, he needs to WQEAuto, forcing him to ult if he has it or simply lose the trade completely against meta mid lanes as his DPS is bad before ghostblade with long cooldowns and below average attack speed and being melee.
All of Zed's strength in low tiers is harass then doing a badly executed all-in, they scream "SAFE, WHY SO SAFE", because they underestimated Zed and communicate poorly, and learn poorly (thats why they are in low tiers, other than just being really casual which is okay, but then they shouldn't be complaining at all)
In higher tiers, in plat-challenger, the strength comes from the ability to have some safe farming against most match-ups with the ability to all-in pretty much every champion in the game if performed well and catching them off guard. He has very snowbally mid game and is weak to certain items to the degree that he simply cannot even bother attacking someone with zhonyas or qss so he does a good job with comps that have strong snowbally mid games like pantheon, graves, jarvan etc. in trying to end the game quickly, or else he has to solely devote himself to split pushing or bronzie poaching in the jungle to have an impact.