Personally, this was one of the attractions GRW had that I liked. .....no class based system and very few RPG-like mechanics (at least in the core game). It gave you the freedom to choose how you want to outfit your player.
I do wish players would have been limited however to what they could carry through a weight system. In other words, as it is now, players can carry two main weapons without limitation and essentially perform two completely separate roles like sniper and assault. .....support (e.g. LMG) and assault. ....etc., etc.
I think if folks were limited to what they could carry in the 2nd slot based on what they choose for the main slot, it would have made for more interesting gameplay in co-op.