"It may sound reassuring that someone watches your back and won't allow mistakes or would help clean up a mess, but you should not keep relying on this anyway."

This assessment totally devalues the experience of having an more senior, more capable colleague to learn from. They are not there to watch anyones back, stop mistsakes, or clean up anyones mess. Rather the point is that the junior member is able to watch the senior person, observe how they solve their problems, and how they approach fixing their own mistakes. It's about tacit learning, not bein nannied/micromanaged.