just my thought and again useing wh40k
the MIXED part would mean the ranges are differnt and while that is versatile it would suck to have only 1-2 units be able to shoot from far away while some are more close to medium.
as a space marine unit that makes more sense since they are able to take the hits and even in close combat stand their ground.
the KO thunderes are almost more like the eldar ( the old ones) where you could sepcailize in a specefic ranged unit.
or in real life - why give a group or archers a few guys with slings and some with rocks to throw and expect them to "adaptive"
they gna get charged and rofl stomped.
so for a "dawrf" army that used to be pretty tough they get rolled especially the ranged units.