Inside front tire wear is pretty common on aggressive alignments. I'm not sure what the stock alignment settings are for the GTO though.
On my Z06, I wore out the inside edge of my stock Goodyear F1SC in 3000 miles. With front negative camber over -1.0 and some slight toe out, the inside edge can drag and wear out very fast. Lots of front negative camber help these front engine cars turn in and corner well... at the cost of tire wear.
Thus, you can wear out the inside front edge very fast, even if the alignment is okay.
I suspect their is a band for the alignment. For example, on the Z06, the front camber can be from -1.2 to -0.2 with -0.7 nominal. I had mine put near the max negative to improve handling. To improve wear, lower the front camber to nearer zero and set toe near zero if that is allowed.
I also have learned, as indicated above, that there is a huge tolerance in "stock" alignment settings giving the dealership a lot of latittude to call your alignment okay. When I had my car aligned, I told the dealer exactly what I wanted (e.g. front camber -1.2, front toe zero, etc)
However, if you corner aggressively, you are going to wear out the outside edge, not the inside. So, I don't agree with your dealer on that one. The outside corner gets most of the work in the corner, the inside edge gets more work driving straight, particularly with lots of negative camber and some toe out, which tends to drag the inner edge down the road.