I saw recently a few games with powerful mercenary rush. And I realized most of the civs has access to strong mercenary/Explorer counter (Spy, Ninja,…) but not all of them. Native Americans does not have a unit like this.
They can send Advanced Scout card to enable Scouts in TC and they counter mercenaries but this card is usually not included in a deck.
I think all Native American civs should have default access to a unit which counters mercenaries/Explorers like a Spy in Age II. Probably in TC or Native Embassy because they don’t have a Church building.