Your logic relies on the weapons not being designed in a way that directly mimics modern firearms.

Exactly compare our first ever weapon made to modern weapons , there are many revolutionary advances and changes so wouldn't the same go for thousands of years of improvements and redesigns ?

No. The design of our modern weapons have always been possible. They may have seemed impossible hundreds of years ago, but they were not. The physics of these weapons is impossible. Period. Though that goes without saying for a multitude of things in Destiny. You're using the same argument I am by comparing it to reality, but you have a different goal for your argument. If you're going to compare it to reality (which I am, from a specifically aesthetic perspective), then it must conform to accepted reality, with the exception being the necessary impossibles. To simplify and reiterate... I'm not here complaining about Ice Breaker... or the Vex Mythoclast. I'm here complaining about weapons modeled after modern firearms, that do not meet the physical specifications of modern firearms.