I agree that this is far too powerful at the moment, and does need downtiering. Plus the damage values are inconsistent. One table lists them as tiers 1, 2 and 3, and another lists them as tiers 2, 4 and 6.
Personally, I think the highest this should be reaching is tier 5 with heavy cartridges, which are energy based and can only be used in power armor.
Yamatai weapons must be treated the same way as anyone else, which means we need to fight the damage creep like we would on any other article.
I think a good compromise on damage would be tier 2 for light cartridges, tier 3 for standard, and tier 5 for heavy.