No matter Vlach should be introduced or not, some your arguments may seem imprecise.
For someone, the area was already covered by Magyars, Slavs Byzantines and Turks in AoFE.
Bulgarians? Slavs. Cumans? Magyars. Tatars? Turks.
Even Goths might cover Magyars and Slavs well in AoC for someone who cared nothing about European history. It depends on how you define the word “cover” so this argument is imprecise.
What did Vietnamese achieve? Conquered by the Chinese for the thousand years?
What did Celts achieve? Conquered by the English in the end?
What did Cumans achieve? Becoming the refugees of Mongol invading?
What did Koreans achieve? A big market of the RTS game?
I do not oppose the civ above being introduced, just mean that it also depends on how you define the word “noteworthy”.
In the history of Romania and Wallachia, the foot archers were the important part. Their Țintaşi (Vlach Marksmen) played a big role in their battles.
Vlachs (or called Romanians) has records enough to design the tech tree, make the campaigns, choose the UU and UT, name the AI leaders, etc. It is actually qualified to be introduced a civ, just worth discussing how the priority it has.
Were Aztec people majority of Mexicans then?
No matter the dynasties of Jurchen Jin, Mongol Yuan and Manchu Qing, the majority of the people were Han Chinese.
To be honest, how special its culture and warfare were is important than how many people there.