No, Carmack has been misquoted a bit on that one.
He directly said "It's almost amazing how close they are in capabilities, how common they are,"
From a game dev standpoint, when both systems are using the same 8-core CPU, same GCN architecture, and same 8GB system memory (- whatever the OS/etc is using), well you DO have systems that are equally capable.
What he's saying is that there won't be games that you can make on one platform that won't be possible to port to the other system. And once you get all the tweaks right, the games should play roughly the same.
Capability ~= performance though. With a pretty stark difference in memory bandwidth and GPU power, you'll be able to move your sliders up a bit on PS4 vs. XB1 as a game dev. It doesn't even have anything to do with 'optimization' AT ALL, it's just : can we render this at 1080p? Yes, okay, can we turn draw distance up? No. Okay then. Etc. With all things being equal, the PS4 will either have smoother average performance, or higher detail settings. The only alternative is a forced combination of framelocking with details moved down to make XB1 playable. Which we may see some releases like that, but doing that risks getting blown out by competing 1st party and better ported 3rd party titles if the differences are stark enough.