Two Handed melee weapons in real life are generally actually swung around faster than one handed weapons in general. The difference is that in real life these two handed weapons are generally kept swinging to keep up the momentum of the weapon. They are very aggresive weapons and are used to knock the opponent's weapon or shield around to force them to keep on the defensive.
The problem is that in Mount & Blade you don't have to keep the weapon swinging around since you can use them just as quickly from a stopped position. In reality if you stopped swinging your two handed weapon around, you'd be at a tremendous disadvantage.
It all boils down to the fact that two handed weapons in Mount & Blade are treated pretty much in the exact same way as single handed weapons. In a way this makes some sense in terms of gameplay because it makes the use of either weapon more intuitive. However, in reflectining how two handed weapons in reality, it makes combat with these weapons very unrealistic.
If you wanted to make Two Handed weapons act more like they do in reality, the speed of the weapon should start out very slowly with the first blow and then progressively get quicker as you swung it around up to a certain point (possibly after the first 3 or 4 swings). This would mean that a player who wants to use a two handed weapon effectively would have to keep it moving and force his opponent to keep on the defensive. If he needed to make a quick block or if he stopped swinging for any other reason, then he would become far less effective. Some players may argue that this would only make spamming swings with two handed weapons even more prevelant but guess what, in reality that is what you do with two handed weapons, spam attacks to prevent the opponent from take the offensive.
Aside from this the other reason why two handed weapons are so effective is the fact that you can swap weapons around too quickly and the fact that carrying around alot of weapon options does not penalize the player with any significant disadvantage. This is simply not how things are in real life.
In reality if you carried a two handed weapon into a fight, you would not be carrying a secondary one handed weapon and shield along with you. Let alone a fourth throwing weapon or second shield. The fact is that players have too many inventory slots and they can switch their items around far too easily.
This has the effect of canceling out the inherent advantages and disadvanatges of general weapon load outs. What was the biggest disadvantage of carrying around pikes or big two handed weapons? That's easy, that would make you vulnerable to missle weapon attacks. But in Mount & Blade, are players who carry around two handed weapons really all that vulnerable? Of course not. They can just as easily bring around a shield and one handed weapon along with their two handed weapon or pike. If they are getting shot at they simply switch to the shield which takes about half a second. Then they can approach at their leisure and pull out their big two handed weapon when they close in for the kill.
If you tried doing that in reality, you'd get a couple of arrows sticking out of you while you sheathed your two handed weapon and then unstrapped your shield from your back and drew out your side arm weapon. Then get shot a couple more times for good measure as you strapped your shield on your back, sheated your one handed weapon and drew out your two handed weapon.
I have no problems with armor not slowing you down very much because they were designed to allow you to move fairly quickly and the fact that their weight is equally distributed on your person. Carrying a pike or tower shield on your back, let alone a pike and two tower shields, however, is going to slow you down and make you ineffective when it comes to a toe to toe sword fight.
Simply put, weight of sheathed or strapped weapons and shields should have a far greater impact on your ability to move and fight than the corresponding weight of armor. Swapping weapons should require the player to go through a lengthy animation, particularly if you happen to be swapping out a shield. Those things take forever to strap and unstrap from your back. The player should need to go through a sheathing animation for their weapon, a seperate one for a shield, then a drawing animation for the weapon they are bringing out, then a unstrapping animaiton if they are drawing out a shield as well. Alternatively the player can simply drop their weapon or shield in the interest of a faster animaiton of simply just drawing out the weapon they need.
As it is now, players are simply too versatile when you allow them to bring around so many weapons and shields by giving them four slots and allowing them to swap weapons nearly instantly. That is why you see so many players carrying around two handed weapons, because they can just as easily bring around a shield and one handed weapon as well to defend themselves against missle weapons afterall. Besides switching between your weapons is a trivial thing. Thus if you can bring around a sword and shield as well, then why not bring out a two handed weapon which are are so effective in melee as they should be. Afterall, elite melee troops using two handed weapons like the real world Huscarls were devastating if they were brought into a toe to toe fight. The disadvantage in reality was that they often got shot down by archers before they could get in close enough to wreck their havoc. In Mount & Blade, however, where all palyers can bring in four pieces of equipment with them with no real disadavantage as compared to sticking to a single weapon (or weapon and shield combination), this is never an issue. Even if you spend all your gold on an expensive two handed weapon you can pick out a free shield and single handed weapon, so what's the point of not doing so?