No, no. I understood your post. What I don't understand is why they would make you pay for a 2.5" rear pipe & muffler to be installed when it would have cost you about the same (maybe less) to have a larger front pipe installed, therefore increasing flow.
The aftermarket exhausts for the VQ25DD (N/A) are 2.5", so I am confused as to why they recommended a 2.5" (even for now) on a turbo that pushes ~0.8bar
I am aware that I am not an expert (far from it), but if you have a large rear pipe and a smaller front pipe and one of them needs to be replaced, logic dictates (at least to me) that it is the smaller one that gets ripped off, not the larger one... particularly if the purchase/installation price is similar...
Please correct me if I am wrong... or have mis-interpreted your post.
Oh, and I agree with what they say about putting a 3" cat-back system on the 2-2.5" stock front pipe. It does nothing but add a little bit of noise