This is the closest I've seen to comparing an All In One liquid cooling system/LCLC to a custom liquid cooler.
The "custom" water cooler in that chart is the Larkooler SkyWater 330, which is a liquid cooling kit (they call it a liquid cooling system) that comes with a pump/reservoir combo, 240mm radiator, some rubber tubing, a copper block, some water/Propylene Glycol mix for the fluid, and various screws and fittings.
That's interesting, if those results are a good enough reference to a custom loop, then it must be a good choice to grab a decent AIO nowadays over a custom loop if you are only cooling the CPU, I mean you can get a decent AIO for the price of the pump alone on a custom loop, custom loops look the bomb, but if you're not too bothered about aesthetics and just want to cool you're CPU then I think a AIO is not a bad buy IMO.