FWIW, my team in AWS had help from UI designers who were cool people that impressed me with their work. We definitely had to push through some needless organizational friction, e.g., they were in a different org and frequently got left out of meetings, whereas we should really have been acting as one team. I don't think we saw it as everyone for themselves, we really tried to make it work and had a good, trusting relationship.
In the end, our leadership changed what we were building so often that all of the UI work was scrapped long before we shipped. We ended up launching a janky console, quickly assembled by SDEs who were racing against deadlines. We skipped virtually all operational readiness work to meet the launch deadline. After claiming the launch win, the director, two managers, and the pm promptly left for other orgs.