No matter how good the ATS is, it will not sell here in the UK. We do not like American cars, we do not like Cadillac's and we do not like their consumer demographics.
I can't recall if they do plan to sell it in the UK or not, but if they do I doubt highly they will get the sales they want. Maybe some clever marketing could push things in their favour, but BMW, Audi, Mercedes will just push right back and assert badge dominance.
Thing is, many qualitative views are not/cannot be taken into account by reviewers. Something simple like the quality of the maps on the Navigation. I don't mean how up to date they are, but how they look, how they take landscape into account, thickness of roads, RTTI, pleasant woman and the colours used. Mercedes' is fecking horrible! Audi's is pretty good. BMW's is best. Does the ATS used GM's system?
My opinion, but if you simply take a look at each system, I'd be surprised if you said the others were easier on the eye. The BMW is a well rounded car, as are Audi's. Merc's to some extent...
My point being, the Cadillac may be a dynamically better car in terms of performance on the track, but I want a BMW or an Audi over it, and that can't be explained so easily.
One could argue a biased view, what with being a Bimmerpost member approaching 2000 posts and a BMW owner for 7 years so far (9 by the time it's bye bye 328i), and I highly doubt I'll be in another marque, unless the Fisker Atlantic is as amazing as it could be. Or the Tesla Model S actually... Mmm...
But, like every time, I will look at all rivals to be sure!