Context: Modern historians debate and argue over historical events. Meanwhile the sage Vyasa dictating the Mahabharata to Lord Ganesha, showing that ancient historians simply recorded massive, made-up casualty counts - something shared across the globe.
you may have read too short a version - the best i can do is a watch some 240 hour video adaptation, which is non canonical as hell, and a russian dub is available online.
as some one who knows it somewhat -
it was a bit more than brothers conflict, think more in line of atla - who should be fire king - ozai or zuko (ccomparison is fair because both are fantasies).
that is mostly heavy exxageration.
depending on “stuff” total death toll of battle could be in range of 100,000. but basically putting any number is just as wrong.