Do we have heights of Shimotsuki Yasuie and Shimotsuki Ushimaru? Even panels that could be used to make an educated guess would do.
Let's try something:
- Most Wano males are huge (around 3 meters and above), exception seems to be Izo (who for some reason has regular height even though his brother/sister is huge)
- But Koshiro again, is of regular height (which was mentioned ad nauseum by many people during Koshiro/Kyoshiro fiasco)
Now, this means one of the following:
- Shimotsukis are shorter than regular Wano citizens
- When Wano guys marry non-Wano people, the children are regular heights
- Wano's climate makes people taller, so when Kouzaburo went to EB, he made smaller children
- Oda is terrible with heights
In any case, Zoro has regular height, so for him being from Wano would require either climate thing or non-Wano marriage thing or Shimotsuki being shorter to be true.