> Every agile project I've ever worked on has had a design doc that laid out architecture, the basic shape of contracts, dependencies and so on. In fact, the agile artifacts(tickets, estimates, epics etc.) have always been downstream of a design doc source-of-truth.

That's not agile.

> A project where all the work comes directly from tickets with no overarching, agreed-upon document on what the end goal is supposed to be sounds hellish.

Maybe this is why so many people can't even try to do agile. It sounds bad. But it works great.