:WP:OVERCAT seems to argue specifically against creating excess categories such as those above, which would be very narrow and only have a few articles each.  By your standard, why would "traditional Chinese objects" fit here when history of technology does not?  The horse collar was developed in China, but its impact revolutionized agriculture in Europe.  I can't see a real good reason to include one and not the other.  If you have ideas for EXISTING categories to add about technology of the mIddle ages or something similar, I'm open to suggestions, but it WAS a significant technological advance for medieval Europe, so somehow that's got to be figured out.