Marty Chinn summed it up pretty well a few comments back, but basically, Devs will push the PS4 as far as they can because that's the only choice they have if they want the console audience, and it leads to better and better looking games over time. Look at Uncharted 1 compared to The Last to Us, or GTA 4 compared to GTA V. The Devs pushed the PS3 as far as they could since there wasn't a more powerful option available. After the PS4 came out, we still got games on the PS3, but they were clearly designed with the PS4 in mind, and the PS3 versions of those games suffered heavily because of it. While it probably wouldn't be as extreme of a difference, I absolutely believe what the OP says about Devs more or less leaving the OG PS4 in the dust, and making the most of PS4K instead, while the PS4 suffers from "considerable sacrifices" that I don't believe would be necessary if Devs further optimized for the PS4, as they had with the PS3.