I was surprised at the lack of regional monks in DE. I was already used to them from HD and WK.
About the topic, I like to think AoE2 is “set in an alternate historical timeline” where all these civs were more in contact with one another and the flow of knowledge such as metalworking and siegecraft was widespread, explaining the technological similarity between civs from all the different continents.
In that sense, some regional variation would be nice as long as all the units are still easily recognizable, as mentioned in other threads.