Over a year in, I’m still very happy with my Dell XPS system, which is the first fully pre-built main system that I’ve gotten in over 25+ years of PC gaming.
The whole “best” parts thing for PCs can easily bleed into the pseudo-superstitious nature of audiophiles. PCs are effectively digital systems. Yes, there are some differences by manufacturer and not all of part “X” are the same, but for the most part (e.g., 95%+) performance is the same. Durability/failure rate differences may exist, but I’m definitely in the camp of spend less and upgrade more frequently (e.g., a 2-3 year cycle) due to the very steep price curve for PC parts, as you approach the enthusiast end. I haven’t had a major part failure that I can recall, besides a power supply here or there because I kept transplanting them into new systems, for years.
My Dell was easily at least 40% off of the best I could do on PC pricepicker for the cheapest variants of the same parts, much less whatever I deemed to be the “best”. Do the pre-builds save cost by using cheaper components? Sure. But they also save costs by volume discounts, supply agreements, and saving on retail channel costs. Plus, for a volume manufacturer, you have the assurance that your specific mix of parts will play together well, which isn’t always a guarantee with a custom.
Overall, I’d say source your own parts if you’re trying to build a bleeding edge system. But if you’re going for mid-range, I good pre-built, at a sale price, is very, very hard to beat.