I don't recall this quote you made being supported by the video first of all. He never said live rock from the ocean isn't a good idea, he said he'd personally prepare it a certain way first. He also didn't say all you're doing is introducing a bunch of pests that will overrun your tank.We don't need to speculate. They just did a 30 week long test with dna testing to back up their data, and live rock directly from the ocean is not a good idea. All you're doing is introducing a bunch of pests that your previously sterile tank is not prepared to deal with, and it will be quickly overrun.
Yeah, you can buy everything you need separately if you really want to or just get it all together fresh from nature and depending on the size of your system you really don't even need to QT it...a LOT of people don't. There's a lot that you simply can not get such as many bacterial strains and natural biofilm unless you use live rock. It's simply not possible at this point in time.