Even with AI, there is a clear difference between juniors and seniors.

None of the things I can think of have anything to do with avoiding problems.

To some degree, having 5+ agents working on different projects is similar to leading a team of 5+ people. The skills translate well.

The senior is also able to understand what the agents do, review and challenge it. Juniors often can't.

And finally, the senior has a deeper understanding of what the business and problem domain are, and can therefore guide the AI more effectively towards building the right thing.