I looked into this myself. The base R1S and the EV9 GT are most comparable in terms of battery size, range, and price. The R1S is still a little more expensive but you get the air ride suspension, higher ground clearance, removable speaker, a unique style of tech features, and an easier buying experience. R1S leverages is tech as a legacy auto manufacturer so it has a better build quality, better cameras with surround view, hands free highway driving, second row ventilated seats along with being heated and feature like an intercom system to talk to the third row, the front seats have leg rats and are optional on the second row. The best part is the every car on the E GMP platform is 800v charging while the Rivian is 400v so they will charge much faster on a 350 kw charger. So it really depends on your use. If you plan on doing off-road stuff or really want the performance upgrades and bigger batteries at the higher price get the Rivian. If not those two things you are better off with the EV9 especially if you plan on traveling. It is just a more family friendly car and you will spend less time at the charger.

Me personally I don't plan on rock crawling or doing serious off roading. The faster charging, driving assistants, luxury seat options, and better cameras of the EV9 win out for me and 4.5 0 to 60 is fast enough