That's how it probably should be. Heavy armor is some beastly shit. Plus I'm sure yer guy will be slow as ass with it on. Maybe you have less weapon slots for heavy too. We don't know, but I'm sure there will be a big penalty for it.
People that need heavy armor, should be the slowest fuckers out there. Although heavy armor would be great for all of you Base Campers holding Noob cannons..! haha BLAH!!
Also, 5-6 shots really isnt THAT many! If the dude is running slower than you that is. Emptying a clip in his ass shouldn't be to difficult.