If the under-dog keeps winning, then they have to come up with a reason for defeating a better force. That shouldn't be too hard, one just has to look at Alexander, American Patriots, the Warsaw Ghetto Uprising, the Viet-Cong, or any other number of outnumbered, out-gunned forces throughout history.
Just to set the record straight...
- Alexander was hardly outgunned. The Macedonians outnumbered the Persians at Issus. At Gaugamela, the Persians outnumbered the Macedonians, but not by much (depends on which figure you use).
- Neither were the American Patriots, really. Plus, they had the home ground advantage.
- Warsaw Ghetto Uprising was brutally crushed.
- The Viet-Cong lasted until 1968 as a guerrila force (different from a conventional army) before they were pretty much destroyed in the Tet Offensive.
Point is, training, equipment and numbers do matter.