ive said it over and over again so ill try it more detalied this time so ppl can understand my point.
humans are on a loosing war. wasting resources is very stupid and considerind their extremely small numbers they have to make each unit count for as many as they can. thats why humans dont have cannon fodder units like the grunts.
this makes each unit fairly expensive, because the armor and weapons have to be the best out there, if humans really want to survive. also with a lot of training in the end humans have just a small but very powerful army. thats what makes each human ground unit better that its covie counterpart.
but costs ruin the whole thing. i remember reading somewhere that the spartans had costed as much as a new fleet and thats why they made the s3 project.
so on one side we have few powerfull and on the other side many weaklings. many have compared humans to starcrafts terrans and covies to protoss but thats just done the bad way. plasma aliens wont be everywhere plasma aliens. protoss are very few in numbers. so covies should be zerg and humans protoss. at least in the cost/numbers/firepower relationship