When they try, they still have to approach the cover. If they overextend, they leave themselves open, and also group up.
No, there were like three dogs in quite partial cover who got hit pretty reliably: Reks, Pudding and Boo Boo. They just needed to shoot more and aim more. Not sure why Brutal AI was so miserable about it.
And opening themselves up is meaningless, your dogs didn't have ranged weapons, were in melee rush range anyway, and the Sectoids were dead either way.
Think zombies, but sectoids.
Zombies are pretty deadly if they manage to overrun you.
Still not enough.
Yah, missed armor effectiveness, too.
Fisticuffs are just bad against so much armour.