You guys are really going to discourage devs posting in these feedback threads if EVERY time we post some info on the game you jump to conclusions and always assume that the way we've implemented any new system is "Omg WTF it's arcade COD" worst case scenario
First off it IS realistic to have players characters increase their abilities over time. It happened to real soldiers, it's going to happen with ours. That doesn't mean it will be implemented in a way that is crazy unrealistic COD level - with vast changes to capabilities and lame perks like guys able to magically crap grenades when they die. The effects of any capability changes will be really subtle, and probably be a max difference of say 10% between lowest rank and highest rank.
We'll likely have server setting to disable some of this stuff for things like competitive play. And we'll have servers set up with min/max rank so players of similar skill levels can play together. But really, the gameplay effects of rank are pretty subtle, and once you experience it you'll likely think it's no big deal.
Regarding the questions on MGs, yes they are more accurate, but also have more/different recoil based on our experiences now firing the real mgs. So firing in bursts will be really important.