When you have multiple people, there's an increasing amount of overhead, from communication, from coordination, needing someone to manage and lead. Now if a single person is able to do the work of multiple people, or even more so multiple people from different disciplines and different teams, then you are gaining much more efficiency. Because you've now replaced 4 people, and then you're moving 4x faster than those 4 people were working together, because there's no overhead required. So now it's actually a 16x speedup. In the same time that it took someone to schedule a meeting with the other team's manager to ask for resources to prioritize time in the next sprint, for someone to review the design and then help out, your superstar already did the whole thing herself after lunch.