I wouldn't say Kakashi is faster than Darui since Darui has shown great speed feats in his fight against the Kin/Gin bros showing that he is able to go close to long range and back incredibly quickly.
Darui was totally surpassed by Kinkaku when he used V2. Kakashi was fighting many of them with ease.
The thing you are forgetting about Raikiri is that its reach is as far as Kakashi can stretch his hand while with Darui's sword as the longer reach.
The reach is not a problem for Raikiri since it can pierce thru anything and we have seen it again in latest chapters against a
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how easily raikiri was able to pierce thru it like it was nothing. Furthermore, Zabuza's kubikiribocho has a greater reach than Darui's blade, yet Kakashi's Raikiri pierce thru him with ease. The thing you also forget here is the sharingan precognition advantage. It's what helped Kakashi to perfect his Raikiri. That's why something like
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would happen
Kakashi can also use
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if needed. This jutsu is even very flexible since the extension depends on the distance between the 2Kakashis and the piercing power is so great that it cut thru V2 tails with ease
Darui starts fights mainly with analyzing and long-range attacks, if Kakashi used a clone Darui's long ranged attacks will expose Kakashi's fake clones.
And why so? Contrary to the popular belief, the clone has the same level the original has. It's just that the chakra is equally seperate in them. Do you think Kakashi's clone is not capable to attack or defend itself? Are you forgetting that Kakashi's clone was able to fight both Deva and Asura during Pain's arc. It
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(probably coming from Asura's missile) and almost
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if not Rinnengan's share of vision. Kakashi's clone was
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with
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(one of the fastest ninja in the manga). Clones can also use ninjutsu as well. What stops him from using doton wall to protect himself if needed? Furthermore, Kakashi also has long range attacks like his
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for example, something he can control. How does Darui dodge that? With the sharingan it's even possible that he could copy the laser circus since it's not a kekkei genkei and i've seen plenty of ninjas able to use it in one of the latest chapters, which shows the difficulty to learn it is not high and thus copiable by the Sharingan
If Kakashi used Doton wall in the fight at any time he will be fucked since that will be obstructing his view providing Darui with the perfect opportunity to Laser Circus him and with the wall blocking his view he will have no time to dodge it, not that he could anyway.
When Kakashi usually uses doton wall, or
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, he directly go for
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(either using a clone, plus hiding underground or vice-verse). So by using the doton wall, it's Darui the one who won't notice when Kakashi subtituated himself with a clone when the original is hiding underground. So Darui would pay attention on the clone when he will come out, use his raiton attacks to destroy it, when the original will surprise him from underground and finish him. If Kakashi even wants, he can use a raiton kage bunshin the time Darui is distracted. Darui hurts the clone and gets paralysed, now himself come out and finishes the job