Matrix level was Tech Demo, think about it as what is max you can do with crowds in unreal. Epic is notorious, they make tech demo to get few “investor bait” buzzwords, then make presentation around it, and never really develop it further. Mass entity was one of such systems, hopefully it will see mature stage.
Also blackboards indeed are maxed out around 200-300 bots. Only mass entity will do more, and its code is quite complicated (in c++).