Rivian made these tie rods criminally small given the usage profile, weight, and torque these trucks have. For comparison the outer tie rod on my 200-series Land Cruiser is over 25mm and it’s significantly lighter.
Any gains would be negligible and massively outweigh the benefit of having a full size spare IMO. Switching to a performance tire would have more noticeable impact.
I dont think the Rivian has external height sensors like JLR uses. I've had my wheels off and truck on a lift and didn't see anything like that. And also those are cosmetic only, dont' really add any functionality. Your wheel has to fit in the wheel well whether you have lift rods or not.
There are lots of great options to treat this area if your worried about. You could use something semi-permanent like por-15 and then top coat. Or annual like woolwax etc. IMO running boards aren’t any additional risk. Just prevent like any other vehicle in the salt belt.