Last hour I had time to test a bit. I played a game with a general and 19 oda ashigaru against a general, 5 yari ashigaru and 11 katana samurai. All were without any experince. I used a simple reversed v-formation and it was enough to kill about 66% of the other stack. Then I tested it with 2 xp every unit. That didn't made the katana samurai much stronger, but the ashigaru were much better -> easy win.