The repeating Roman design had 2 flaws:
-wasn't as powerful
-Too accurate, which is actually bad as it was wanted as an Area of Effect machine-gun style effect. No use hitting same target 3 or 4 times.
Saw a working recreation of them in a documentary, pretty amazing
however, since it's D&D, and magic and maybe cultures who's tech advances in their own bailiwicks are far ahead of ours...who knows, maybe they solved the problem?
(always note, other universes/peoples may have tech BETTER than ours, even if in more simpler areas, like weapons/armour: 10,000 years of trial and error, plus magic, plus different mental abilities/outlooks could have huge difference)