Great questions. As always, it depends. Because my design team is small (5 people) and colocated we are able to work together “owning” the ideation and the iterative process. Each designer still is responsible for the artifact or tasks that help meet the user stories and sprint scope.
Thanks to Design Research we have data that informs our design decisions. However, there is always room for design intention and intuition in our process. Because we work fast and ship continuously, we validate the bigger questions but most of the time have to rely on our expertise for the smaller design decisions. We then gather feedback from actual users, and loop it back.
All of this has worked for my team, and for the time being. I am not sure if and how it could scale to larger teams that are spread across timezones. I have found that my team’s process work for us, BECAUSE we are all here.
Glad to chat about this. Over a beer of course.