In a discussion of the 3ed Uncharted Empires on the DakkaDakka forum lord_blackfang makes an interesting statement that “The RC confirmed that they got a list of units to make rules for.”
I am not sure where he got this information, maybe on facebook (I am not there), but if it is true it invalidates any arguments that removal of some units were driven by the rules changes.
In fact, my understanding is that there was no stampede and no chariots among the units provided by Mantic for the Herd theme list. According to a post by @mattjgilbert we should thank Kris Kaspner (one of the playtesters) for inclusion of the Minotaur chariots that we can use now for a “merger” of those two missing units.
That being said (and despite me personally not liking the verdant and especially earth units joining the herd beasts) I am pleased that at least Mantic does work with the Rules committee and listens to them. That’s much appreciated.