No, the Nakhtu-aa are heavy infantry - the 'dismount' terminology is purely MTW-speak for 'change battle mode'... they are heavy infantry in mode 1, but mode 2 is heavy inf with added javelins. Human players can handle this well, the AI can't, so the 'standard issue' is without javs, even though in reality they often did fight with javelins.... hope that makes some sense It's similar to what I did with tribal spearmen/tribal missile spearmen.

That's the one big bugbear with the MTW engine - give a unit a missile weapon and it goes to default skirmish mode, and the AI gets confused about how to use it. If the coding-fairy granted me one free wish for altering the engine it would be that one - put the decision over skirmish/engage at will/hold formation into the unit_prod instead of hard-coding it.