Update 13 December: the MacBook Pro has gone back to Apple, so MPG cannot retest, but it might be that the macOS 10.12 update fixes the performance issues.
A few days ago I reported that the MacBook Pro performance quickly degraded in Photoshop. This curiosity bore no explanation did not settle with with me, nor did an external fan have any effect on performance (the “too hot” theory). So I kept thinking about it.
Another fact comes to bear: three of the Macs could not complete the Photoshop Lens Filter test some or all of the time, and two could never complete it.
Recall that the 2013 Mac Pro had awful GPU driver bugs for the first six months or so of its debut—Apple does a lousy job testing GPU driver support. [Well, a lousy job on just about everything, as MPG has shown repeatedly in a series of Apple Core Rot posts and articles.]
Accordingly this seems like a GPU driver bug is at work, perhaps introduced in macOS Sierra, and having nothing to do with the 2016 MacBook Pro. With Apple’s poor software QA, this theory makes the most sense of all.
MPG has a hunch that the MacBook Pro performance degradation is a GPU driver bug, perhaps one that leaks memory and thus rapidly degrades performance. If so, a fix in a release of macOS is possible, perhaps soon.