How much control can your classmates have over your own GPA? What percentage of 'control' over your GPA is up to you vs. your teachers, parents, classmates, and everyone else? I put those in order intentionally, as I think your classmates are below teachers and parents on the hierarchy.
Disincentives group learning, collaboration, teaching each other.
Many good cases to have a strict zero sum competition but you won’t see collaboration in these (eg olympiads, competitions). That’s fine for a short term event but for long term learning in a persistent social group it seems good to encourage collaboration