Two handed weapons are slower, however, this doesn't mean they are worse off for it.
Actually, it does. Not only are they slower when striking, they also cripple your movement to a large degree when striking. Much more so than when using one-handed weapon strikes.
It is much easier to land an attack on a moving enemy in range when your power attack is slow, by giving you time to adjust your angle.
This is an argument for, "If you svck, it might be easier for you to land a blow with a two-handed weapon as opposed to a one-handed weapon."
Block runner works with two handed weapons as well. This will allow you to run circles around your enemies during a quick reflexes time slow, just like a shield user would.
Yes, Block Runner works with two-handed weapons. So what? It just means that you can do something worse than someone who's using a one-handed weapon + shield. To me, the point of Block Runner is to have block up at all times because you can't always avoid enemy attacks (Mostly due to areas you're fighting in such as cramped dungeons with little space to move or difficult to maneuver). When you block a strike with a shield, it is far more effective. When you dodge an enemy attack via Quick Reflexes with sword and board, you can land more hits and when the damage gap isn't much between a one-handed weapon and a two-handed weapon, it means you're doing more DPS.
Furthermore, with a one-handed weapon and shield you can resume blocking far quicker so Quick Reflexes kicks in when it needs to kick in. The better movement speed while striking with one-handed weapons and the quickness to resume blocking helps your footwork tremendously when compared to using a two-handed weapon with similar technique.
Great critical charge out right kills lower level enemies and helps mobility.
Lower level enemies are one shotted by mere one-handed strikes, sprinting if need be, and far quicker too. If the damage gap was actually significant, this would be somewhat of a positive for two-handed weapons. Since it's not, well, it's not much of a distinction/advantage.
Ok well, the first perk in the block tree, 20% block, is fine for two handed users on master, especially considering after quick reflexes and even block runner, attacks will simply be dodged anyway. Why do you need that much block with your shield? I'll never understand.
Well, if we're going to go that route, technically you never ever need to block then. Ever. In which case dual-wielding is the better choice, by far.
Heck you can even use Shield Charge with a two hander is you block right before impact.
I doubt that's intentional behavior and in my experience with it, it's far from consistent behavior. (That means that it's very difficult and inconvenient to have it fire off every time you want it to as opposed to using it the proper way with a shield.)
ALSO two handed weapons have a higher chance to stagger enemies by power attacking compared to one handed users if said enemies are blocking or not.
Chance is the keyword. It's not consistent behavior. You know what is consistent behavior? Shield bashing. Works far better than hilt bashing with two-handed weapons (Greater reach, fires off quicker) and far better than an inconsistent stagger on power attacks. It works even better when enhanced by meditating on the word Fus.
As far as end game damage numbers are concerned, when we're talking weapons that do over 300 damage, 1h or 2h it really really really won't matter what your using by then as every single enemy will fall within seconds. So in the beginning of the game, two handed users have it really nice due to higher damage, paired with more staggering attacks and toward end game you just kill more and more enemies with 1 hit with great critical charge.
If we're talking about the beginning of a play-through, then one-handed plus shield will work out better because it provides better defense (Which you need in the beginning if you're playing, say, Master difficulty) and greater openings to which attack an opponent (Due to swing speed and swing movement speed, better bash). If we're talking about end-game, it provides better offense than two-handed weapons short of some situations where the difference would be counted in milliseconds.