This is what I believe:
1. I think Zabuza's taijutsu/kenjutsu is better than Darui's, the only reason why Darui beat out Suigetsu is because Suigetsu turned himself into water when being hit, which then he got electricuted and numb because of Darui's channeled lightning. Zabuza is a legendary swordsman, I would say Darui's a decent-pretty good kenjutsu user who could hold his own for a decent amount of time if they engaged. I don't think Darui would cut all the way through the Executioner blade because when Sasuke used his lightning enhanced blade on the Executioner blade while Killer B was wielding it, it only cut through a little and then it took the Raikage's power to snap it. Even if Darui did cut through it, since Zabuza is more skilled, he can probably draw a little blood from Darui and rebuild the blade. I found this,
You must be registered for see links
2. Laser Circus is a move where the user can bend the direction the lasers move in, however it requires accuracy to do so to hit the target, so if Darui can't find Zabuza then he can't aim to hit him. Even if Darui randomly aimed his lasers around the area, the chances of one of them hitting Zabuza is very low and if one was coming Zabuza's way, just like Kakashi sensed and saw the shuriken Zabuza threw at him, Zabuza could just jump out of the way because it's not a barrage of them like there were against the Gold and Silver brothers.
3. Darui's suiton isn't comparable to Zabuza's, true he can create a wall with it(Water Wall), but that can only lead Zabuza to use a Water Clone with it, which Darui would then channel lightning through the water just like he did against sasuke and destroy the clone, which would lower his guard because he would think he defeated Zabuza (clone feint) and allow Zabuza to sneak up behind him and then, just like Kakashi, be kicked into the water and then be caught in a Water Prison. If a 3 tomoe Kakashi couldn't keep up, then Darui roughly around the same level but without sensing abilities and a Sharingan definetly can't.
4. If Darui were to channel lightning threw Zabuza's Water Dragon or Giant Vortex Jutsu, it would only lead Darui to getting even more damaged and the most, slightly hinder Zabuza because if Zabuza used Water Dragon or Giant Vortex Jutsu, it wouldn't stop the technique, it would go through it (channel lightning into it) which would enhance it, making the force even greater when coming at Darui and flow all the way back to Zabuza, and since both are long range techs, that would give Zabuza enough time to jump out of the water, seeing the lightning travel through it, and protect himself. So that would be an invalid argument because not only would Darui be physically damaged by the water, but electrocuted by Black Lightning, putting him on the verge of death.
Basically since Darui doesn't have sensing abilities, I doubt he can pull off beating Zabuza if Kakashi with Sharingan and his dogs to sense and react barely could.
You must be registered for see links
for more reasoning, you have some good points, but I still think Zabuza has a higher chance.