^
https://www.youtube.com/watch?v=kPIhvfal12g
that's a nice tear down
If you look at standard D5 or DDC pumps (most commonly used in custom loops) and how much flow/head pressure they can do, you will see the difference.
They are also made of materials that allow much longer and quieter operation.
Another thing is radiators - the Swiftech and EK are making theirs from copper. the ones in those CLC are made mostly of aluminum. In fact, some coolers by asetek are made completely of aluminum - both cold plate and radiator.
On the same channel, you can find the latest review of the of the 1080 FTW Hydro and how adding memory to the cooling affects the cooling performance.
back to our analogy hyundai i30 vs audi A3 (sedan). Both have about the same space, both help you to get from A to B. but there is a huge difference between them. now imagine that the audi is priced the same as hyundai.
While you are right that those kits do the job and do it quite well. But since the prices of kits from Swiftech and Alphacool got to the same level - they are a clearly better performers (temperature to noise). not to mention expandability, option to swap/replace components.
That's the reason I call the CLC from asetek crap. only relatively to those. on it's own in a vacuum, they are kinda fine and nice.