Same conundrum for me, except the bed is out (Excursion, and that's MY bed). A hitch hauler was nearly perfect for what I did for a long time, even with the 990ADV. But now there are at least two bikes.
The self-leveling would be an amazing benefit whichever way you go. But Tom makes the likely accurate observation that no matter which one is on the carrier, it's the other one you'll want to use. You'll be motherfucking that choice every time you have to drop the hitch hauler bike to get to the one in the bed. Rivian may not have a place at the table yet in terms of aftermarket support, but there are those bed extenders that double as a ramp and work pretty well. I may actually have one from a GMC if you want to try to retrofit it.
Final answer though - I'm with Tim. Though it is an additional piece of equipment to register, maintain, store, etc... it's just the best answer. I'm slowly coming around to it myself, and it's painful because I like a simple, self-contained one-piece unit. But it isn't simple anymore (or... again). And that's okay, the benefits largely outweigh the negatives, just have to adapt.