Absolute Duo

A Shield is actually the best weapon one can handle, because you can attack+defend at the same time without leaving attackable openings. And if the Shield is big&sturdy enough (like 3-6 cm thick, 50 cm width and 70 cm length; iron/steel) you can easily break one's skull with a single strike with some training of your arm muscles.

It also comes with disarm-ability if the form is not straight but round(deflects projectiles/blades easily and creates an opening to attack while the enemy might even tumble away) or additional attack ability if you add blades/thorns onto the sides/front.

The only downpoints are the short range(melee basically=your arms length - half of your upper arm + the shields body structure[thickness+handle+shape]) and the bluntness of the weapon(meaning you need to put in a lot of strengh and/or your body weight to attack efficiently and decelerates the shield alot because of the large surface area and weight[depending on the material,even a small shield weights up to 5-7kg and large ones weight like 15-20 kg!], so hard training is needed to turn it into the deadly weapon it is indeed).

You....don't really know anything about fighting, weapons, or shields...do you? The shield you described (30mmx50cmx70cm) would weigh roughly 81 kilos (180 lbs)? Even the strongest men in the world would not be able to utilize such a mass as a weapon, they use masses like that for weight lifting.

Secondly is, a 20kg object in one arm, is going to be slow. Very slow. Trying to attack with such an object is invariably going to unbalance the "wielder" and make him vulnerable to anything.

Can a shield be a weapon? Yes. It can be very effective at it as well. However, there is a reason why the shield has never been considered a "primary" weapon in the history of man kind: It is inefficient. It weighs more than a comparable bludgeoning tool like a mace, a flail, club, etc, and would wear out the wielder far faster than a more efficient tool. Anyone trying to swing a 10 to 20 kilo weight strapped to one arm, is going to tire themselves very rapidly. Especially compared to the enemy who is armed with a sword, mace, or any other conventional weapon.

Secondly, is reach. A Shield has extremely little reach. How are you going to hit the swordsman, if he is always 4-5 feet away at the end of his own blade? Polearm where you have to cover 8-10 feet of distance?

A Shield is actually the best weapon one can handle [...]

Not really. As you mentioned, your example of a shield would have a very short range. The weight it would need to be efficient would also make it slow. A decent spear-fighter could easily use both of these things to his advantage. As would a fencer.

I don't think the "best weapon" question can ever been adequately answered, since environment plays a to big role. For example, it's generally assumed that a katana-fighter needs to be three dan/master-levels higher than a naginata-fighter, since naginata/swordspears and similar blade-on-a-stick weapons have high range, high speed and decent striking power... but even then, there's the downside of needing a lot of space to fight. A naginata becomes a lot weaker in enclosed spaces like corridors, and could easily loose to a naginata or shortsword.

A Shield is actually the best weapon one can handle, because you can attack+defend at the same time without leaving attackable openings. And if the Shield is big&sturdy enough (like 3-6 cm thick, 50 cm width and 70 cm length; iron/steel) you can easily break one's skull with a single strike with some training of your arm muscles.

It also comes with disarm-ability if the form is not straight but round(deflects projectiles/blades easily and creates an opening to attack while the enemy might even tumble away) or additional attack ability if you add blades/thorns onto the sides/front.

The only downpoints are the short range(melee basically=your arms length - half of your upper arm + the shields body structure[thickness+handle+shape]) and the bluntness of the weapon(meaning you need to put in a lot of strengh and/or your body weight to attack efficiently and decelerates the shield alot because of the large surface area and weight[depending on the material,even a small shield weights up to 5-7kg and large ones weight like 15-20 kg!], so hard training is needed to turn it into the deadly weapon it is indeed).

Best choice though if trained properly, and you can even use a second weapon in your sub hand to distract the enemy during fights(mainly people would think the weapon is not the shield but rather mistake whatever you have in your other hand as the main threat and though your main hand! That allows you to easily distract with the first blow and go in for the kill with the 2nd )

Captain America

A Shield is actually the best weapon one can handle, because you can attack+defend at the same time without leaving attackable openings. And if the Shield is big&sturdy enough (like 3-6 cm thick, 50 cm width and 70 cm length; iron/steel) you can easily break one's skull with a single strike with some training of your arm muscles.

It also comes with disarm-ability if the form is not straight but round(deflects projectiles/blades easily and creates an opening to attack while the enemy might even tumble away) or additional attack ability if you add blades/thorns onto the sides/front.

The only downpoints are the short range(melee basically=your arms length - half of your upper arm + the shields body structure[thickness+handle+shape]) and the bluntness of the weapon(meaning you need to put in a lot of strengh and/or your body weight to attack efficiently and decelerates the shield alot because of the large surface area and weight[depending on the material,even a small shield weights up to 5-7kg and large ones weight like 15-20 kg!], so hard training is needed to turn it into the deadly weapon it is indeed).

Best choice though if trained properly, and you can even use a second weapon in your sub hand to distract the enemy during fights(mainly people would think the weapon is not the shield but rather mistake whatever you have in your other hand as the main threat and though your main hand! That allows you to easily distract with the first blow and go in for the kill with the 2nd )