While your basic argument
While your basic argument that a leader must lead by doing that which the competition isn't is relevant you picked the wrong vehicle to target for criticism.
Does MB, BMW or Audi put their most advanced technology in their volume vehicles? The answer is, no, they don't. They reserve the cutting edge items for the top end models where price isn't as significant an issue.
Were Cadillac to do what you suggest with the ATS they would have had, at best, a difficult time keeping the price of the vehicle competitive in the segment.
Goal one is to demonstrate that Cadillac can match or even top the best in the class using comparable technology. That establishes the credibility with buyers in the segment. It does Cadillac no good if they can't get potential buyers attention and in the showroom door to look. Once in the door you can't scare the buyer away with a price that asks them to take on faith that the Cadillac is worth more without a proven track record. They have to establish credibility and deliver on the promise first. Pushing the envelope with technology comes later, after they've established the credentials with the buyer.
I don't see GM holding Cadillac back here. I see them taking a measured and pragmatic approach to reestablishing the brand in the market. If they can hook and hold on to converts at the entry level they stand a better chance of keeping those customers. Once they have the loyalty established they can move these customers up the ladder to higher end models where the leading technology can be applied with less concern to cost.