If we think about it, there are more or less 4 basic forms of melee weapon usage, and I do think they all have slightly different role to each other enough to justify their existance:
2 Handed Weapons: High Damage, No Defense bonus
Dual Wielding: Below normal damage but x2, slight defensive bonus
Weapon and Shield: Normal Damage, big defensive bonus
Single 1 handed weapon: Slightly above normal damage, greater accuracy, slight defensive bonus
But really this doesn't even matter, the largest part of the reason this choice exists is basically because people like options for their character and people consider dual wielding cool, therefore, it is a good option to include. It's a staple of the genre and I don't see "but its impractical!" as a good reason to remove player choice, as long as it gives sufficient advantages and disadvantages for all the choices.
Personaly i want defence/Ofence to be a much deeper than just one stat ala D&D, you do get hit or you dont.
Where the 4 weapons styles can have more that hi damage/defence.
Each weapon type having diferent stats and properties. for example:
A towe shild is big and heavy, if they get flanked the have penaliers to defence from the flanked side, a large shild or medium becasue they are smaller and lighter dont suffer from this. the end result could be something like this. With rating form 1-100 in each area just to give a number that has no meening.
Fighter 1 Mace and Small shield- weapon speed 2 secs. Crushing bonus 50, Block 30, Perry 10, Dodge 15.
Fighter 2 Mace and Medium Shield- weapon speed 2 secs. crushing bonus 50, block 50, perry 10, dodge 5.
Fighter 3 mace and Tower shield- weapon speed 2 secs. Crushing Bonus 50, Block 80, perry 0, dodge 0. Flat Foted (if you are flanked, you resive a 0 block from the flanking oponent)
The same way we cann add properties to each tipe of weapons, For example:
A flail its all offence with no perry, block, dodge, and high block daamge (to stamina), and high crush damage, (damage stoped by the armor).
A sword, has high presition damage, with good dodge and perry.
an so on with axes, maces, hamers, Stafs, Daggers, etc.
with stats like Weapons speed, Weapon range, arch (can a swing cleave trogh more that one target with a swing like a 2H gratesword can hit 2 targats in front of him?), perry, dodge, Block, and what ever else it feels right.