I take it those are gaming systems? I thought I knew a little something about PCs, but those are different animals indeed.
Water cooled? Graphics systems must generate a helluva lot of heat.
I'll admit to being a dinosaur - one of my first encounters with computers was an IBM 360 mainframe that had water pipes underneath the floor to cool it down. That computer plus the disk storage and printers wouldn't fit in my living room! The first laser printer I ever saw was the size of about six filing cabinets. It had its own programming language, so sometimes there were some interesting things coming out of it as people learned how to use it!
They sound like great all around systems, for gaming or video editing given the high core count cpu's he's got in there. Or any task that can make use of lots of processing cores. Performance gpu (graphics cards) are great for gaming but can help in other situations as well. Streaming, boosting video editing, offloading some rendering jobs. Probably has more $$ in that 3090 than I have in my entire system lol.
Water cooling is one way to go. It does pull heat quickly away from hot components, if it's slightly over radded (using multiple larger radiators than what's actually necessary) it can allow a user to run more fans, more cooling surface and therefor run the fans slower/quieter and still achieve good cooling. The single fan on my aging gpu sounds like a fricken tornado when gaming. Water cooling still has some limitations, when the system's been running awhile the coolant will reach equilibrium in terms of temp and like any air cooling can only cool as well as ambient air temps allow. If the room is hot the system is going to run hotter. Vs active cooling like a peltier system (like ac for pc components). But those have their own issues with condensation and needing to work around that.
Or you could go with big air coolers, usually my weapon of choice.
6.4" tall x 5.4" x 5.9" weighing 2.64lbs. 2 fans, one in front and one in the middle. Even when my quad core cpu is overclocked by quite a bit and under heavy load the cooler really doesn't struggle much. Stays slow and quiet. I finally got the fans to spin up harder and was able to hear them but I had to turn off every other fan in the case and run the processor overclocked under a stress test on a hot day. A ridiculous situation it would never run in normally. But not everyone likes coolers that large or bulky, they can be a pain to mount. I just install my processor and ram to the motherboard out of the pc case, then set the cooler on a table. Flip the motherboard upside down and lower it onto the cooler.