Having slower athletes on the team is great.
Back in school, my small public high school had an enormous track team. When the girls and boys went to meets together, we always needed two buses.
1. Larger team camaraderie.
2. Larger cheering section.
3. Opportunities for novice field events meets, JV/Frosh/Soph races at XC invitationals.
There was a kid a year younger than me who as a sophomore ran 27/28 for 5K. By his senior year he ran 17:20 and ran at two state meets -- cross and outdoor 4x8 relay. Had we cut him, he never, ever, would have dropped 10 minutes for 5K, become a team captain, or turned into the emotional bedrock of the cross-country squad.
That, and it's always fun to have the best JV cross team around.
And that's appropriate. "Citius, Altius, Fortius." Swifter, higher, stronger. This sport is about competition, but it's also about improvement. Why do we have youth races? Masters races?