''Military colony'' type building? And maybe the citizens you train there can build a few more of the Lusitanian/Celtiberian buildings

There might be enough justification for a heavier elite infantry. It is not described what weapons they had; but swords are possible. We know the Cimbrian cavalry used swords. But also the women of the Ambrones, so they don't seem to be only for cavalry.  

We worked on some of this in historical and can continue to do more if you think it's necessary! @TheCJ

That's the idea and I think we can even go a bit deeper than simple embassies, as Duileoga made a few good designs:  

84 score Reasoning: 0ad anthropologist

Think of it like this: They are too important to chop wood and mine metal or stone. Their experience is much more valued in battle, so they are sent to battle more often by their superiors. Hence, lower gather rates to compensate for this historical truth. And since they spend more time on the field, doing repairs and building army camps, their build speed remains constant.

Dont get me wrong, i build/repair with my elite infantry, i just find it funny that they consider themselves too good to break stone blocks at the stone mine but see no problem laying the same blocks in the construction site . But yeah i see your point.