Not really you having to be watching every squad on the field at one time all the time and no one can do that and thanks to pathing and dumb shit riflemen will not always move fast enough to get out of the way when your in cover like there running into each other and rifle nades still wipe in green cover.
No they don't. Green cover reduces incoming damage so unless you rifle squad is already almost dead it will take 40% reduced damage and not be wiped.
Also if you miss the most obvious grenade tell in the game along with it's travel time then welp I don't really know what to say. The abusive thing about defensive stance is that it has no draw backs because you can reposition almost instantly.