I’m no expert, but I have a different opinion. Immune systems need practice, although serious pathogens are not recommended.
Which parts of the immune "need practice" and why? What changes with macrophages or neutrophils if the body encounters fewer pathogens? What exactly changes about the behavior, number, or effectiveness of dendritic cells due to a lack of exposure to a given level of pathogens? What changes about the complement system? What T-cells are affected by this and how? Which B-cells?
No, you are not an expert. And your "opinion" differs from observable reality.