Nobody said the pump alone was noisier. You want to run your AIO with just the pump? I didn't think so.
The noise levels for practically any 240-420mm AIO is always going to be louder if you factor in not only the two fans that will be running but the addition of pump noise as well. Even coolers with two fans on the heatsink are typically quieter because unlike an AIO they are buried inside the case rather than being faced directly against an opening to the outside. It's really no different that taking an alarm clock that is ringing and putting it in a box. Sure, you can still hear it, but it's going to be quieter than it was before.
This is obviously not directly comparable but it is in fact representative of what you'll find, across the board, doing similar comparisions. Note that practically every AIO except the Floe Ring 360 is louder than the nine air coolers in the comparison. And the Floe Ring is a 360mm so clearly it can run it's fans a bit slower while still maintaining fairly decent performance since it has a lot more surface area AND an additional fan.
Overall, AIO coolers are much noisier, with 50-60db not being uncommon under load. Sure, you can tune them for quieter operation but you are going to lose a significant amount of performance that way. By comparison, The NH-U14S or NH-D15 can be run at full speed fans and with a decent case the noise levels are low enough to be conversational. Spin it however you like, complain about the full speed 12v operation, the fact remains that most AIO coolers are going to have significantly louder cumulative noise levels with it's two fans and pump than an air cooler is. At least if it is a decent quality cooler with good quality fans.
And I don't ever have to check to see if the damn thing has ruined my hardware today or not. Nor do I have to guess if my thermal issues are due to a bad pump. Nor will it cost me another 120 bucks when something does go wrong with my cooler.