The novel did say that, but if you re-examine the book, we mostly see civilians being hunted down, and those with the surname Wen. This means that he doesn't necessarily hunt down those who use gui dao. He didn't even go after Xue Yang, a famous known criminal following the dark arts. I'm pretty sure Jiang Cheng only hunted down people who reminded him of Wei Wuxian and the Wens, not gui dao users or criminals.
If Jiang Cheng were really hunting down dangerous criminals, then he should have hunted Xue Yang down, but he didn't. He probably knew that Xue Yang was too powerful for him, since the novel said he doesn't like starting fights if he knew he couldn't win, and went after those weaker than him. Those people were most probably cheap knock-offs of Wei Wuxian like the "Know-It-All" of Qinghe (maybe that's why Jin Ling had such a violent response to him, he probably just imitated what Jiang Cheng does) and civilians.
I don't think anyone else could have used gui dao. Gui dao is the path of the ghost/dead humans. This would mean surrounding yourself with dead corpses, which is already disgusting as it sounds. No normal person would voluntarily hang out with dead people. The majority of people are either terrified or don't care about the dead. Wei Wuxian is a special case because his empathy extends to everyone, even the dead! We can assume he probably bonded with the dead during the time in the Burial Mounds. No one could have experienced what he did during those 3 months in the Burial Mounds and came out alive and sane. Literally, no one would be willing to give their body for another random soul to inhabit, in case of possession. We only see Wei Wuxian do this because of his mastery over Empathy and his empathy for the dead. No one would sympathise with the dead like how Wei Wuxian did.
Not only that, but it takes skill to be around the dead, the dead are there because they have lingering resentment, if you do not know how to redirect that resentment, then the corpses may harm you. Not every ghost is like A-Qing, most of them are aggressive and harmful.
Maybe let's say, you don't want to spend time with corpses, you just want to use them. That also requires skill. The reason Wei Wuxian uses music to redirect the resentment is because music can be used to stir up resentment or calm down resentment. Basically he uses it to control the corpses. The clapping, snapping fingers, punching the ground, and etc were only used to awaken the resentment in the corpses. Every time he needed to calm down the corpse, he needed to use whistling, humming, or playing an instrument. That's why he uses music more, since it can do both, and it is more flexible and efficient. With music, he can give more complicated commands since it contains multiple noises instead of just one simple sound and the sound can travel further with an instrument.
Also, I don't think he needs to clear his mind using music, I've never read anything about cleansing his mind in the novel, I think that was just an Untamed thing (yet another thing the Untamed butchered 😭). Using resentment has never affected him before in the novel. His cultivation style has never corrupted his mind. So he doesn't need to clear his mind. Wei Wuxian is very emotionally strong and intelligent. This is also one of the other reasons, why only he can use gui dao. Because of his mastery over his own emotions, especially over resentment. Wei Wuxian is a character that lets go of resentment. He isn't affected by the resentment because of this. Compared to Jiang Cheng, Xue Yang, and Jin Guangyao, who were consumed by resentment until it ruined their own lives, Wei Wuxian has never let resentment control his life.
If there really were people trying to imitate Wei Wuxian, we can safely say they are doing a really bad job. There is a certain text in the novel that supports this.
“Ahem. All right, it was Wei Wuxian who started the trend, but he successfully refined Wen Ning—that is, the Ghost General,” he said. “To be honest, I always wondered who came up with that nickname. It’s so stupid. Anyway. Others tried to mimic him but could only produce poor imitations at best. They ended up going down a deviant path and set their eyes on the living instead, coming up with living corpses like this.” He concluded, “They’re failed replicas.”
We can assume from this text that there were people who wanted to use gui dao. But they failed and ended up going onto the demonic path instead. An example of this would be Xue Yang. Xue Yang studied Wei Wuxian's notes but he still failed to use gui dao. Let me tell you, Xue Yang is actually quite talented and smart, so if he of all people failed, then most probably no one could succeed. Xue Yang lacked empathy for the dead, that's why he couldn't use gui dao. So he turned to demonic cultivation instead.
If you ask me, the easy path would be mo dao instead of gui dao. If you compare the two, mo dao is easier to accomplish. And from the text that I showed above, it does seem like those who originally wanted to use Wei Wuxian's gui dao ended up using mo dao because it was easier compared to it.
