Looking at the block diagram of X299 which have been released so far, it seems the storage linked from the PCH (DMI 3.0 using PCI 3.0) which seems to be a similar layout to X99. However, if we look at the Z270 layout again it’s in the same format but they have boosted it to 8 PCIe Lanes (PCIe 3.0) to the PCH. So, it’s fair to assume the X299 will follow the same methodology.
However, if you look at the X370 layout from AMD you have x4 (PCIe 3.0) directly from the CPU and then a further expansion of x4 PCIe 3.0 from the X370 chipset.
AMD are currently rumoured to have a HEDT which is due for release soon, again this is only rumours but it would make sense as they have the fully-fledged Naples server platform coming soon. So, it would make sense to compare the storage options against two level playing fields.
So, I really wouldn’t call AMD’s offerings weak as in theory it has the same bandwidth as the current Z270 boards and more than the current X99 systems (This excludes add in cards)
However, please correct me if have misread any of the diagrams incorrectly.