I sort of loved that angle in the books that the Yeerks weren't exactly experienced at warfare and had only been doing it since around Vietnam. Made it all a little more plausible, that humans have sort of evolved as fighters, and by this point it was all sort of picked up by osmosis, even 13-14 year old kids grasped the basics of guerrilla warfare and hit-and-run tactics. Where the Yeerks (aside from the original Visser 1) were more about clumsy brute shows of force, just through inexperience.
And how the Andalites had been warriors for some time, but also had that prideful thing going on, they weren't really down-and-dirty do-whatever-you-have-to, Alloran aside, they sort of took the high road in the early books, until it all hit the fan and they got corrupted and desperate too.
A cool way to go with it, like humans might be technologically inferior, but we're basically really scary when backed into a corner and forced into fighting.