A lot like chefs have a variety of knives or musicians have lots of instruments, each piece of gear is rated for a specific use. Level 4 plate is resistant to larger rifles while smaller armor ratings are for knives and pistols.

And no matter where you live, shit is fucked right now. Either Trump or Putin is going to nuke something and the only civilized countries seem to be between them. Good luck in your civilized country while you have it!