The problem isn't necessarily power draw but one of software support inside the headunit itself. It's only designed to support USB devices of classes X & Y (e.g. iphone and mass storage device) and simply doesn't know WTF to do with a hub.
I've been somewhat annoyed by this problem for quite a while. The best option is a MANUAL USB "Switch" so you can run a cable to two different locations and flip a switch / push a button to toggle between which one of those cables is actually attached to the head unit.
My current Pioneer unit has a pair of USB inputs which is great, but if you want to use Android Auto vs. Apple Carplay, you have to use specific ports. So if you wire up one port in the glove box and the other to the front near where a phone mount would go, and then you later switch from Android to iOS, you have to pull the radio back out and switch which USB extension is plugged into Port A vs. Port B.
It's really consumer-unfriendly.
Then there's alpine who just give you a single port. What if you want your phone but also want a USB stick full of tunes? Alpine would have you go pound sand. (Or, fill your phone with your tunes, but then you're stuck fighting with ****ty iTunes to load music on it instead of being able to just drag and drop files to a drive in whatever folder tree you prefer.)
My biggest gripe with the whole iTunes paradigm is that it doesn't offer you the ability to sort a given artist's albums by release date. Nope, you get them alphabetically, so if you don't remember the name of the album but just remember it was "two albums ago," you're screwed. Super annoying, if you're a person who still prefers to listen to an album at a time instead of the shuffle garbage that all the kids do today.