I want to connect many fans to a single ARGB header
How many fans are you going to use? And what MB did (or will ) you get?
You need to do some homework first. 1) Check the fan to see what Amp they will draw. 2) Check the MB manual to see how much Amp the argb header can provide. Because for most of newer MB, the rgb header can provide either 2Amp or 3Amp, if these Fans will draw more power the header can provide, you kill the rgb header ( or the MB). That why you have been told you should buy the hub, because the hub will be powered by the PSU, then the fans will be powered by the hub.
And if these fans will draw less power, you can connect the fans into the MB argb header.