So would the RT cores in all likelihood - be a waste - if they don't provide similar memory bandwidth as the XsX IMHO. And I really think they only need a cheap SSD cache in the lockhart - the size of a game, so less 100GB - as part of a hybrid mechanical drive, along with providing the external SSD port that interfaces the VA IO, so they can upsell the highly profitable external SSD modules to the entry level buyers.
On the memory side of things, 560GB/s might sound like a lot, but when you consider the XsX and lockhart are intended to share a CPU spec (according to rumours) then that CPU is consuming a lot of that 336GB/s (of 192bit bus unified RAM) when it doesn't have an additional 10GB GPU pool with 560GB/s to asymmetrically access,, too and might risk starving the ~4TF RDNA2 GPU
Edit:
Also if the CPU memory use(IO and SSD, BCpack features) is supposed to be the same on lockhart(as XsX) to stop next-gen games being held back by the ~4TF console, then of the rumoured 7.5GB available to games on lockart - presumably of 10GBs, 1GB per channel with the same 2.5 use by the OS - then we would expect the same 3.5GB of the 7.5GB to be used by the CPU, leaving just 4GB for the ~4TF, so bandwidth to keep the GPU fed might be even more crucial with such a small dedicated pool.