Yes body armour will stop hits from the good old 7.62 ak stuff, and the new dragon armour does a great job, but for the 5+ its mainly for the amount of body covered as well, i know most times you aim for center mass etc, but bullets do go wild, and hits in arms and legs can course shock and blood lose etc...
5+ modern armour
4+ sst amour ( not movie type, but cgi show ), this shows more on arms and legs etc
And its 2+ with extras "wink wink" for the new grizzly exosuits...