I have seen that diagram and it is more confusing than helpful.
Summing 24! PCIE 3 lanes, the SATA ports and whatever bandwidth the USB add up to vs DMI results in an absurd mismatch of bandwidth and in no way is it reasonable to assume that reflects reality.
Also, this directly contradicts that claim:
https://hardforum.com/threads/intel-dmi-3-0-bottlenecks.1930465/It seems to me the chipset offers a whole 24 extra lanes to play around with, which can easily be spread over enough M.2 ports and additional storage controllers to satisfy practically any reasonable use case(a 20 drive storage server on z390 not being one of those).