They are completely different routes to gaining communication.
If you're in no signal areas, the Starlink will be your best bet, assuming you have a clear(ish) view of the sky.
WeBoost is fantastic in low signal areas, but primarily for voice/text instead of super fast data (as the WeBoost is not MIMO).
It *could* be powered off of one of the roof switches, assuming you order a shorter cable, as well as the appropriate adapters to go from DTP plug to the 5521 connector (and can waterproof the 5521 connection).
The problems come when you attempt to use the provided 15m cable with 12v power, because the amp draw is exceeds what the tiny (28AWG?) wires in the cable can carry, and it'll start cutting out and rebooting. This is why the provided AC adapter outputs 30v. For my setup I'm running a 5m cable (purchased on Amazon with appropriate 5521 weather resistant ends) as well as running a 12v-24v step up converter. At 24v it works even with the 15m cable. Looking back at it after the fact, I would have ordered a 12v-48v converter and allowed the wiring to run at an even lower amperage.
For my set up the WeBoost external antenna is mounted on the roof rack and the Starlink will be as well (currently on a magnet mount)