But everything you're saying about the difference being small is not panning out so far. So really one side of the argument is a measurable difference being visible right now on current games and the other side of the argument is rampant speculation based on wishful thinking.
1. You are basing the comparison on launch games built on changing hardware that are often rushed out in time.
2. There are several sources of evidence that show that X1's tools were a mess before launch whereas the PS4 had more mature tools.
3. A CD Project Red dev came out and said that MS ends up being more open about their tools and shows devs more shortcuts later on in the generation whereas people have to create a network of devs in order to find the best ways to develop for Sony hardware.
4. The difference in the end, in my eyes, is probably going to be 900p vs. 1080p with the same effects. AC4 was like this, for one.
5. People usually don't count this but Kinect Sports Rivals is one of the nicest looking games on either console, and its running at 1080p on X1 whereas before they were planning to run at 720p, showing that the tools increased in quality enough to let them hit a better target.