Lord Haseo said:
It’s pretty goddamn unreasonable to believe that you can choke someone to death with The Force (even over massive distances) but choke someone to unconsciousness. Also when choking someone they are knocked out and you have to continue the choking before they eventually die.
Choking someone is incredibly unsafe. If you do not have intent to harm you should not choke someone because even if it’s just for “knocking them out” there’s a chance the windpipe will collapse entirely, killing them. That’d look real good on Vader’s monthly review wouldn’t it? No, it makes much more sense for him not to choke Luke at all if he wants him alive.
Regardless, is he able to use choke while fighting? Even as a sword master he has to be very aware of Luke’s every move to keep his defense up. The only times he uses the force in the duel is when he has breathing room from Luke’s attacks. First after knocking him into the carbon pit, and then later when Luke is regaining his composure out of swinging range. There’s no reason to assume he could use the force like that mid-swing like they do in the PT. Luke uses the force once while Vader is busy dealing with steam in his face. The power level of the OT is not in any way comparable to the PT or the EU. It is much more subdued.
George clarifies at one point that the “weight” is a metaphor he used to convey to the actors that there was a lot of energy and power that needed to be controlled. The wild swinging and twirling seen in the PT style duels is a great way to lob an ear off or get a lightsaber through your leg. The more composed two hand styles seen in the OT conveys that these people are fully in control of their weapons. Vader is supposed to be physically very strong and so we see him knocking Luke off balance with one hand, and occasionally taking one handed swings while still controlling his weapon safely.
The point is not that some magic decree from heaven says lightsabers can only be held two handed. It’s that a lot of power is needed to control it properly, and for the most part that means two hands and a proper stance.