I think a more fun team bonus should be the following:
Inca Team Bonus: Suicidal units deal +100% damage to units and have +0.5 more splash radius.
This should affect Petards, Demolition Ships, Flaming Camels, and Saboteurs, and make Incas a consideration for team games played over water.
Edit - perhaps this is a bit OP on water. If so, we could edit it to just say “+100% damage to land units”, or make the bonus a flat number, or make it just +1 splash radius with no damage increase. (So demos still kill a lot more crossbowmen, but they cannot single-handedly kill fire ships of the same age.) I was also hoping this would be a way to make Tatar flaming camels more viable in team games with Inca allies, which was why I suggested the damage bonus.