I think the biggest misconception is that Cadillac just arbitrarily "decided" to price the ATS comparably to the 3 series. This is false.
In the past, even when benchmarking a competitor, GM has built vehicles while looking for ways during design to undercut the cost of their rival. Usually this means heavier or lower cost materials, which allowed them to offer a similar size and featured product but for less money. With the ATS, the cost factor was mostly ignored during the engineering phase, instead focusing on weight. In fact, the design team were given the mantra "Every day, every engineer, every gram" during development. Instead of building the car to meet a price point, they did what they needed to in order to make a car that genuinely compared to or exceeded the competition.
As far as lease cost, residuals and incentives, all three are not compatible. High incentives hurt resale value, which is why in the past, BMWs have held higher residuals than Cadillac. Over the last few years this has started changing however- Edmunds.com gave the award for "Best Resale Value, Sedan over $40k" to the CTS, and "Best Resale Value, Luxury Brand" to Acura, Lexus and Cadillac.
See full list here
People seem to want it both ways. They want tons of incentives on the new cars to make them affordable, but then want a high resale value- the two are incompatible. Cars with high resale values have good reviews, high demand and low incentives. If you want affordable leases on the ATS, then you should hope sales are brisk and incentives are not needed. THAT will lead to high residuals and low leasing.