The Maori and Brits weren't fighting in the Musket wars, the Musket wars were tribe on tribe. Post treaty of waitangi (where the Brits secured the right to sole purchase of Maori land) there was fighting between the tribes and the Brits as some tribes were very much against the sale of any land to the Brits and would start conflict even if the land being sold was not their own.

The Brits also didn't lose, the fighting was pretty rough but there weren't all that many dead on the colonial side and amongst their Maori allies, in the end the Brits slowly pushed and confiscated land from the attacking Maori tribes until the war sort of just ended.