Yea the Sheetrock will do a bit smoothing out inconsistencies. Especially if you go 5/8ths. Next time make sure you crown all of your studs in a wall the same direction. Modern lumber is garbage. Good practice. Like I said metal studs would work great since they are not structural and straight as an arrow. They make lvl studs too. Super straight. Very expensive. Metal is pretty easy to work with. Reduces moisture wicking in damp basements and easier to frame slab to ceiling when there is inconsistancies

Sheet rock I just call it rocking.

Are you rocking both sides of the wall? If that’s the case and it really bothers you you can shim out. If perfectly straight basement walls are really that’s important you should frame with steel studs. That would solve the issue

They will just be skids under your 2X deck? Then whatever you do is fine. Scab with 2x4 both sides of you want. You probably don’t have to do anything. Toenail a couple 5” exterior screws if your feeling generous