http://www.eurogamer.net/articles/2...nity-graphics-lock-for-parity-on-ps4-xbox-one
Technically we're CPU-bound. The GPUs are really powerful, obviously the graphics look pretty good, but it's the CPU [that] has to process the AI, the number of NPCs we have on screen, all these systems running in parallel."
We were quickly bottlenecked by that and it was a bit frustrating," he continued, "because we thought that this was going to be a tenfold improvement over everything AI-wise, and we realised it was going to be pretty hard. It's not the number of polygons that affect the framerate.
We could be running at 100fps if it was just graphics, but
because of AI, we're still limited to 30 frames per second."
What he is saying here is that the AI is limiting the FPS to 30FPS. He is not saying the AI is limiting the resolution.
What you have missed is that the CPU bottleneck is not the reason for 900p.
Below is the explanation for 900p..
"We decided to lock them at the same specs to avoid all the debates and stuff"