Does zed need kills in lane to be useful later?

Define 'usefull'. He will be a serious threat the moment he gets Dickblade, but if he isn't snowballing that might not be enough to decide the game before everything outscales him.

I'd say he needs kills or at least needs a really big CS advantage, but that would probably led to multiple kills.

Alot of it isn't to do with riot but the actual players.

Annie morgana brand and zyra where never intended to be supports, the same with Leona and blitzcrank.

Well, as someone who mains zed i can gladly help you out on that one.

Zed is an assassin who relies on early Snowballing, not as much as most other champions but he too Needs an Advantage to really get going. So i would say yes. He doesn't Need to rack up a 12/0 kda but he does Need a few kills or at least a massive CS Advantage. You Need to get ahead in gold, you Need to be superior in pressure so you can safely roam without being chased down.

Zed has the ability 100-0 an unprotected carry even when behind if he lands 3 shurikens, all with their first hit for full damage. So he can pretty much always oneshot, if played well.

However, he doesn't have the ability to nearly oneshot someone from the range of your average Adc. And later on, getting a perfect combo is nearly impossible with tanks and supports.

If you're catching people out, you don't need much at all, but even then your targets might be tankier than an ADC or mage. If your going for teamfight assassinations, you'll need some kills up your belt, or very good Cs. Or bad enemies