There's also the issue of shield use not being represented properly. A swing from a long lever like any 2hand weapon could be shield smashed by a competent user, to force the 2hand fighter to turn his hips back into the swing a bit and be exposed for a quick stab or swing to one side.
And on the 2h swing arc issue, these weapons are, again, long levers. Think about a halberd. If the halberdier is inside the range of a 1hand-and-shielder's weapon, then any block or parry will land much closer to the pivot point on the haft, the users hands. That means the swing arc would get stopped much earlier, which for the 2h wielder is the most exposed time. That's when their hips are turned the most to create the power for their strike.
I don't know if any of the above is necessarily implementable in the game, but it is what happens irl.