I take the fairly quiet rc be a good sign for 4.16, but honestly, rc2 is often fairly calm. That's probably because people are taking a breather after the merge window, but also simply because it might take a while to find any issues.
But let's be optimistic, and just assume - at least for now - that it's because all is well.
The diffstat is fairly odd, but that often happens with small rc's just because then just a couple of pulls will skew things easily in one or two directions. This time the patch is about one third architecture updates (arm64, x86, powerpc), one third tooling (mostly 'perf') and one third "rest". And yes, the bulk of that rest is drivers (gpu, nvme, sound, misc), but those drivers are still distinctly *not* the bulk of the whole patch.