Thanks Richard.
Initially I did try all of my impact guns. That didn't do it for me.
I've not seen the chisel nut split solution before. Let's hope I never have to try it! Awesome to know though.
Here's what I did do though. 60v Dewalt reciprocating saw + 5 blades through the shaft. I was hoping the one half of the shaft would just pull though. BUT NO, there just had to be a flange at the bottom. What ended up working was a slight flat spot, 3 vise grips, and a 24" breaker bar.
It does seem crazy that a two year old truck has experienced this much deterioration. It was local to the strut though. None of the other fasteners I had to break were difficult at all. Perhaps water can sit in the top of the strut and accelerate the aging? I did pack the area off with grease in the event I ever need to take it apart again.