Simple, as the title says. Give us the option to designate a weapon as an off-hand, primary, or neither via right clicking the weapon. It isn’t a huge annoyance but having a weapon in your OH that is also a primary can be slightly annoying.
For example: most people by now use their Warhorn or something to get a swiftness boost whenever possible. When switching it out you have to right click the weapon in your inventory and re-equipt as off-hand if it can also be used as a primary, else it defaults to primary. It can get tedious when you do this often.