An example of combat ineffective rates in real combat

[Aeraaa]

Generally infantry toughness in the game seems random. I've seen infantry squads being shot and shelled in the open for a turn with no or one casualty and I've seen them wiped out with a single salvo or lucky artillery shell in other insances(I still remember a japanese 155mm shell wiping out an 8 man soviet mechanised rifle squad that I of course commanded...).

And I generally think of casualties as dead and wounded, with the sole exception of the few stragglers disappearing from a badly hammered unit, or the ones that surrender. Rate of casualties seems very accurate to me tbh...

[Imp]

Generally infantry toughness in the game seems random

Not completely, yes their are a lot of random factors but experience plays a big part.
Try playing with the same units one side set to 65 experience & the other 120, actually that wont work they will be more accurate to
Buy the above & switch weapons off or modify so cant fire back. now use them as target practice & you will discover the experienced guys avoid more incoming.