The only reason to buy a pre-built PC is if you don't have the patience to do a little bit of research and to assemble it. Its honestly far more simple than it sounds. There isn't much you can really mess up or do wrong. (especially if you have at least watched a youtube video or two)
The benefits of assembling it yourself are:
-Generally much cheaper
-Quality control over what goes in your pc
-Better warranties, as every part has its own warranty. Some of them can last 10 years. Whereas a prebuilt is the whole pc for usually 1 year and additional time costs a lot. Dealing with the individual manufacturer support is not really any different than dealing with the custom builder (ie cyberpower) support. The only difference is you will have to do a tiny bit more work in discovering what part is defective and needs to be replaced. Generally, the builder (cyberpower) would walk you through some troubleshooting over phone so they can determine what is wrong and what you need to send into them (and it may require you to send the entire pc back)
-Experienced gained doing it yourself. You will be able to better upgrade and maintenance your pc if you know a little bit more about how it works. That alone is worth a lot.
As for cyberpower itself, they arnt much different from other builders, except id imagine they pay their employees minimum wage who are building it, because ive heard of multiple complaints about things being installed incorrectly when they receive it. Im sure its not super common, but as large of a business they are, they likely dont have much talent working for them at the assembly level. Im sure they would be no better than any average person at it.