So I am totally admitting I have no clue how D&D has changed the rules in 5E, but you used to be able to wield longswords (just for example) in each hand while dual-welding. Same with a rapier or any other one handed weapon. Did Two-Weapon Fighting change where you can only wield light weapons? Longswords just used to be versatile weapons meaning you could wield them with two hands if you wanted, but could just use it one-handed. Same with battle-axes, etcetera. I am assuming since it gives values for one-handed damage they just haven't implemented that function as of yet, or am I just not figuring out how to accomplish wielding them as one-handed for Two-Weapon Fighting style?