the Chinese Ming Dynasty is still the biggest unfinished design part in AoE4 right now (which says something very positive about this game). While all Dynasties have 3 buildings, Ming is missing it. The Grenadier on it’s own is situationally interesting, but just not worth getting it (anymore). All in all the opportunity cost is just too high.
Ming Dynasty in total grants you: A special “super castle” (if you picked Spirit Way before), a situational AoE unit, 10 % hp and 5% faster gather rate with ancient technique.
That is just too expensive to get now and the speed boost of Yuan Dynsty is arguably better.
Instead, I suggest adding a new building, that can be build 3 times like the rest of the dynasty buildings:
Each building grants 5% extra max population (10 each in 200 regular games) and automatically gathers taxes from adjacent buildings (with a small aoe radius).
This reflects the great wealth and population growth during the Ming Dynasty.
In gameplay, you can only afford Ming if you are already at your population limit and still have more ressources. The biggest issues at this stage are just how you need to field more military and the taxes that are not picked up in front bases or that are isolated. These buildings alleviate both problems and offer a great incentive to actually invest so much ressources into a second Landmark.